Russian spy attack: British troops deployed to assist nerve agent probe

Personnel from the Royal Air Force, British Army and Royal Navy were among those sent to Salisbury on Friday, a Ministry of Defence spokesman told CNN.

London's Metropolitan Police tweeted that the public should not be alarmed and the public health advice remains the same. It explained that the counterterrorism division had requested assistance from the military to "remove a number of vehicles and objects from the scene in Salisbury town center."

Former Russian spy Sergei Skripal, 66, and his daughter Yulia, 33, remained hospitalized in "very serious condition" after being poisoned earlier this week, UK Home Secretary Amber Rudd said as she visited Salisbury on Friday.

The pair -- believed by authorities to have been deliberately targeted -- were found slumped on a bench near a shopping center on Sunday afternoon.

Detective Sgt. Nick Bailey, policeman who also was also exp fell ill, is in serious condition, but is "conversing and engaging" with visitors, Rudd added.

Authorities earlier revealed 21 people had received medical attention in the aftermath of the incident, but only three people were still being treated Friday.

Identifying the source of the nerve agent continues to be central to the probe but so far, Rudd has refused to name any potential culprits.

"We will have to wait until we're absolutely clear what the consequences could be, and what the actual source of this nerve agent has been," Rudd said. "At the moment, our priority is going to be the incident, which is why I'm here."

Western intelligence services consider Russia a leading suspect based on previous attacks that used a similar substance and method, a Western intelligence official told CNN. The official cautioned that the investigation was still in its early stages.

If a Moscow link was proved, it would plunge relations between the West and Russia to a new low, and would call into question the British government's ability to protect UK residents at home.

On Friday, Russian Foreign Ministry Sergey Lavrov said Russia was ready to assist "any investigation" but that it was "not necessary to hurl unfounded accusations on TV."

Earlier this week, a spokesman for the Russian embassy in London described comments by UK Foreign Secretary Boris Johnson -- who vowed a "robust response" in the event that state involvement was proved -- as "strongly anti-Russian." The spokesman said Johnson's comments were an attempt to politicize the affair, and attacked the media for aiding the UK government's efforts.

Police say they know the nerve agent used in the attack, but have declined to say what it was or how they suspect it was administered. They called on anyone who visited the area on Sunday, including a branch of the Zizzi restaurant chain or the nearby Bishop's Mill pub, to come forward with any information that might help them piece together what happened.