UN investigating reports of chlorine attacks in Syria

"Most alarmingly, the commission has received multiple reports, now under investigation, that bombs allegedly containing weaponized chlorine have been used in the town of Saraqeb in Idlib and in Douma in Eastern Ghouta," near Damascus, Paulo Pinheiro, chair of the UN's commission of inquiry on Syria, said in a statement issued in Geneva.

The panel also expressed "deep concerned" over the escalation of violence in rebel-held Idlib province and in Eastern Ghouta, Pinheiro said.

The White Helmets, a volunteer rescue group, said three of its members and six others were injured by chlorine gas attack in Idlib's Saraqeb on Sunday night. The group posted several videos on social media showing men coughing and being put onto stretchers.

Two media activists who spoke to CNN from the nearby town of Kafranbil said they were told that the chlorine attack in Saraqeb had been launched from Syrian helicopters.

CNN could not independently verify these claims or videos. The Syrian government has repeatedly denied using chemical weapons.

"Over the last 48 hours, the scale and ferocity of attacks has increased dramatically resulting in multiple reports of civilian casualties & airstrikes that have reportedly hit at least three hospitals," Pinheiro said Tuesday.

"The commission remains committed to fulfilling its mandate to investigate and document all human rights violation(s) occurring in the context of the Syrian armed conflict, regardless of who commits them."

The UN statement comes the day after the US State Department said it was "gravely alarmed" by allegations of a chemical attack by Syrian forces.

"We implore the international community to speak with one voice, taking every opportunity to publicly pressure the Assad regime, and its supporters, to cease its use of chemical weapons," spokeswoman Heather Nauert said in a statement Monday night.

Earlier Monday, the US accused Russia of blocking a UN Security Council statement condemning Sunday's alleged chemical attack in Idlib. Russian UN Ambassador Vassily Nebenzia fired back, accusing the United States and the United Kingdom of "slandering" Russia and "spreading a mountain of lies."

On Monday, the opposition Syrian National Coalition condemned what it described as a "barbaric onslaught" by Russian and Syrian forces in Idlib province in recent days and demanded UN action.

Observers say Russia has ramped up its air campaign in Idlib after one of its fighter jets was shot down by rebels in the province on Saturday. The pilot ejected from his aircraft but died following an exchange of gunfire on the ground.

Russian-backed Syrian government forces began to escalate their military offensive against rebel-held areas, including Idlib province and Ghouta, last month.

The Idlib area is home to more than 1.1 million of Syria's 6.5 million internally displaced people, many of whom escaped other formerly opposition-held areas after they were overrun by government forces, according to UN figures.

Hundreds of thousands are trying to escape the intensified assault and are seeking refuge at makeshift camps near Turkey's border.