Desperate migrants keep coming. Now vigilantes are threatening the welcomers

"You can't tell me to leave. Only the police can tell us to leave," says 22-year-old Spanish volunteer and Mare Liberum sailor Isa Krischke, facing off with a bald, olive-skinned man wearing a red puffer jacket.

"I am the police," screams the man, the veins on his head bulging. He brings his face to hers, grinding his teeth as he stares her down. Krischke backs up and the crew decides to scrap plans to disembark at Mytilene, the capital of the Greek island of Lesbos. Police don't arrive until after the boat has left.

One man who helped drive away the Mare Liberum, told journalists: "Greece right now is under foreign rule!"

"They are human but so are we," he said, referring to the crew.

It was a sentiment CNN heard echoed across Lesbos: angry locals who seemed to believe foreigners -- NGO workers and migrants -- were swamping their island.

The incident last Thursday is part of a spate of nearly daily vigilante attacks that appear aimed at driving away humanitarian workers like the Mare Liberum crew, who monitor the Aegean sea for human rights abuses against migrants. Locals and humanitarian workers describe witnessing physical attacks, harassment and intimidation against those who offer help to migrants -- with apparent impunity.

Days earlier, CNN came across a gathering of men on motorbikes, wielding sticks near the island's power station. It was one of many nightly gatherings of local men who have decided to take the migrant crisis into their own hands, according to aid workers and locals.

One man told us to leave the area.

"This is dangerous," he said, identifying himself as a policeman.

"You must leave immediately."

A bus of uniformed police officers stood yards away, cloaked in the pitch-black night.

A masked man, who identified himself as Tony, said the meeting was for people worried about the situation on the island.

We asked him if he felt the vigilante attacks were justified. "I think it's not. We're all humans," he said. "But you know some people do it ... Maybe. Some people do," he went on to say.

The shield of Europe

The wave of violence against humanitarian workers on Lesbos began as Turkey announced on February 28 that it had opened its borders to migrants bound for Europe.

Ankara was reneging on a 2016 agreement to block the passage of millions of migrants into Europe. Critics slammed the latest development as a geopolitical maneuver, seeking to pressure Western countries to support Turkey's latest offensive in Syria. Turkish people overwhelmingly praised the decision. The country houses more refugees than anywhere in the world, a reality that has taken a toll on its economy over the years.

In Greece, the European Union's first port of call for migrants leaving Turkey, land and sea border areas immediately swelled with newcomers. The once-tranquil islands of the East Aegean -- Chios, Samos and Lesbos -- received 1,200 undocumented people in just two days at the beginning of March. Greece reacted with force, controversially suspending asylum applications for a month and forcibly intercepting most migrant movement on land and sea. Last week, the EU pledged 700 million euros ($802 million) in aid to Greece, including 300 million euros ($343 million) for border infrastructure.

EU Commission President Ursula von der Leyen praised the "tireless effort" of Greek border and coast guards, saying: "This border is not only a Greek border, it is also a European border... I thank Greece for being our European aspida in these times," using the Greek word for shield.

Greece's Prime Minister Kyriakos Mitsotakis defended his government's actions in an interview with CNN's Richard Quest, saying that "Europe is not going to be blackmailed by Turkey."

Greece had "every right to protect our borders," he said, adding "we have not used any sort of excessive force."

Lesbos, which already had the greatest concentration of migrants in the country, received the largest portion of the newcomers, according to UNHCR officials. More than 600 migrants have arrived there since March 1.

The island re-emerged as an epicenter of a global refugee crisis. Sentiments, already at fever pitch, boiled over.

Checkpoints and violence

Humanitarian organizations are increasingly worried about how to keep their workers and volunteers safe.

"There have been repeated attacks on journalists and humanitarian workers by angry mobs and vigilantes," Nickolas Panagiotopoulos, International Rescue Committee (IRC) Senior Area Manager for Lesbos and Chios, told CNN early last week.

As a result, Panagiotopoulous "reduced" the organization's staff presence. He warned about an impending humanitarian "vacuum" that could worsen already "deplorable" living conditions for migrants on the island.

The UNHCR's senior most staff member on the island was attacked when she tried to assist a boat with families trying to disembark, according to UNHCR spokesperson Boris Cheshirkov. The UNHCR transit facility for new arrivals was burned to the ground, preventing aid workers from receiving newcomers. As a result, the new migrants camped on the island's northern beaches for two nights, huddling around fireplaces for warmth before they were detained by Greek police.

The violence reached an "unprecedented scale" over the last week, says Panagiotopoulos. "I have never seen the islands like this."

The IRC, and several other organizations -- including Médecins Sans Frontières (Doctors without Borders) -- say they have considerably reduced their operations in the aftermath of the violence.

MSF closed its clinic at the island's main migrant camp for at least two days, throwing migrants living in squalid conditions into further limbo.

"We are very concerned. The government needs to do more," said Panagiotopoulos.

Workers at the One Happy Family center, a children's school and psychosocial center for migrants on the island, burned to the ground, according to workers at the center on Saturday. Images posted on social media show the center in flames.

The cause of the fire is unknown, but the incident further spread fear among humanitarian workers.

Several times over the last week, vigilantes set up roadblocks around the port city of Mytilene, particularly those leading to a large migrant camp in Moria village, a ten-minute drive away.

Suzanne Whitehead, executive director of the US-based Help International, says she was attacked by groups of angry people twice while trying to deliver medicines to unaccompanied migrant children. At one roadblock, "people in masks were carrying bats. They shone a light in to see who we were so I kind of gunned it through," says Whitehead. "They came running after us."

At the first of two road closures she went through, Whitehead says police were standing nearby and did not intervene.

Konstantinos Koloros, a social worker and anthropologist on Lesbos, recounts stopping at one of the road closures: "They stopped me in my car. I opened the window and I said 'what do you want?' And they told me, 'Are you Greek?' I said 'of course, I'm Greek. I speak Greek as you can see. But why do you ask?'"

"They said 'Go, go. If you're Greek, go,'" says Koloros. "It was like a checkpoint."

"My (foreign) colleagues have been at home for three days and ordering food deliveries," he said during an interview with CNN last week. "This isn't imaginary. It's happening. People got beaten. Cars got broken and people are leaving."

A divided island

Many in Lesbos condemn such tactics. Last Saturday, a group of locals staged a demonstration at the port condemning vigilante violence and singing peace songs. It came days after a mass demonstration in Athens in solidarity with migrants.

NGO workers CNN spoke to said police failed to intervene when conflict arose with local residents. Greek municipal police referred CNN to the national police force for comment. CNN has not receive a response.

The island's courts are taking action against vigilantes. A court on Lesbos recently found two local residents guilty of making threats against a prominent human rights activist.

"The mass media around the world say that the inhabitants of Lesbos are against (the refugees.) But the inhabitants of Lesbos are tired," says Sophia Koufopoulou, a Greek-American anthropologist member of a local organization.

"They cannot take on their back all of the refugee problems of the world. Because this is what is happening."

Ballooning migrant population

More than 21,000 asylum-seekers live on Lesbos, just under 20% of Greece's total migrant population, according to UNHCR figures and government data.

A group of Lesbos islanders were nominated for a Nobel Peace Prize in 2016, a year after the 2015 European migrant crisis, when hundreds of thousands of migrants traveled through the Turkey-Greece waterway, with many ending up on the island's shores.

Despite being in the throes of a national economic crisis, acts of solidarity washed over the island.

But over the last year, government data shows that the migrant population on Lesbos has tripled, in part due to a six-month-old national government policy limiting migrant movement from Lesbos to the mainland, according to Tasos Balis, adviser to the Mayor of Mytilene.

"We never had more than five to six thousand (migrants) living nearby our city and in the city," says Balis. "But in the last six months, no one is going back to the mainland and more and more people are getting stuck here on the island."

Nevertheless, he applauds Greece's latest crackdown on migrants. He says that until last week, the government did not "do anything to support our day-to-day lives."

Mytilene was built for around 30,000 inhabitants. Now it has over 50,000. Municipal buildings are covered with Greek flags and banners demanding the island return to normality. "The islands are ours," says one sign hanging off the columns of a theater.

Up on a hill, the Moria migrant camp is a sprawling encampment where a rank odor fills the air. A river is strewn in garbage. A terrible smell rose from the matted grass as we navigated between tents.

The camp, with a maximum capacity of 2,200 people, houses around 18,000, according to UNHCR spokesman Boris Cheshirkov.

"We have been seeing that the situation has developed to a critical point in the last months," Cheshirkov tells CNN. "And we have been warning that the situation will escalate and that the island communities can no longer face this on their own."

The encampment extends out of the UN camp into olive groves where thousands live in makeshift wooden huts they built out of wooden pellets and tarpaulin, hammered down with nails. People here have no access to electricity or water. They must wait for hours to use a bathroom, and sometimes spend an entire day queuing for food.

"I had no idea it would be like this," says 50-year-old Iraqi migrant Chaker Mahmoud. "I would have preferred to have died in Iraq than to live like this."

Migrants stream down to Mytilene from the camp every day. Suitcases in hand, they flock to the port hoping to mount pressure on authorities to be shipped to the mainland.

When riot police try to corral them out of the town last week, a protest transpires. "Moria not good! Moria not good!" chant the largely Afghan protesters. "We want Athena, Germany, Paris!" Chaos ensues as riot police chase migrants up and down the harbor.

An Afghan man leading the chants, 23-year-old Rafi Hakimi, turns to a group of journalists. "Moria is not a place for humans," begins his impassioned plea. "To the people of Lesbos, I'm so sorry. We're all so sorry. We just want freedom. We don't want Moria."

Wide-eyed locals leave the harbor's coffee shops to watch the scene unfold. Years ago, tourists flooded the port. When they were replaced by migrants, the islanders prided themselves in embracing the newcomers. Now locals wonder if civil unrest will become the island's new norm.

Police on Lesbos

Svenja, 24, who CNN agreed to refer to only by her first name for safety reasons, said she was walking a friend to the port last week when she found herself among a crowd of migrants being driven out of the harbor by police.

Disturbed by the scene, Svenja remarked aloud: "Is this how we speak to each other?"

Suddenly, she says, a police officer ran towards her, grabbed her by the arm and pulled her to his face, screaming out expletives.

The German volunteer says she told him: "This is against the law, you have no right to touch me."

"He said 'there is no law anymore' and then he pushed me away," Svenya tells CNN.

What followed, according to Svenya, was an assault. One police officer pushed her against a wall, she says, hit her on the knee and demanded she "go back to her country."

"I said 'I have every right to be here. This is Europe. I can be here. I have every right' ... And when I said this, they turned around chased me again and then one was pulling me, the other was pushing me," recalls Svenya.

"F**K you, There is not law anymore (he said) -- and that's the truth."

The police did not respond to CNN's multiple requests for comment.

Mytilene's adviser to the mayor says the municipality condemns the violence that humanitarian workers have been subjected to but chalk it up to long-simmering grievances on the island.

Koufopoulou and other humanitarian workers say they doubt that vigilante and police violence are spontaneous.

"There is a perception that the NGOs are bringing refugees here, that if there were no NGOs, there would be no refugees," says Koufopoulou. "If the government wants to stop the attacks on the NGOs, they can."

She describes the vigilantes as a "small but dynamic group (that) have created a para-state" on the island.

Marooned off the island

At Mare Liberum's hiding spot, ship captain Philipp Hahn and his crew must row their lifeboat to get to the pier. They have had no way of refueling, because they have been unable to dock at the island.

When they were first subjected to harassment, a group of angry men doused the ship with petrol and threatened to set it on fire, they say. Now they are anchored in a scenic bay, where they have been appealing to their embassies for help.

After their third attempt to make landfall failed, they say the police declined the crew's request for protection.

"I asked them what do they think is their job if not securing public spaces? They could not give a really good answer," says Hahn.

For now, the crew -- like the people they have come to help -- are stuck, neither able to get what they need, nor to move on to safe harbor.