The opposition Syrian National Coalition demanded the United Nations take immediate action Monday to stop what it described as a "barbaric onslaught" by Russian and Syrian forces in the northwestern province of Idlib amid new reports of a chlorine gas attack on civilians in the rebel-held area.
The White Helmets, a volunteer rescue group, said three of its members and six others were injured in a chlorine gas attack in the Idlib town of 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.
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.
Russia retaliates after pilot shot down
Observers say Russia has ramped up its air campaign in northwest Syria after one of its fighter jets was shot down by rebels on Saturday. The pilot ejected from his aircraft, but died following an exchange of gunfire on the ground.
Russian airstrikes in and around Idlib have killed at least 16 people and wounded dozens more in the last 24 hours, according to the UK-based Syrian Observatory for Human Rights (SOHR). Many are in critical condition and rescue missions are underway, SOHR added.
The strikes were accompanied by renewed rocket fire and shelling by Syrian government forces, according to SOHR. The two activists CNN spoke to described the attacks as "manic."
The White Helmets said Sunday that the strikes hit a hospital in Maarat al-Numan. Video recorded by rescuers and activists showed infants in incubators on makeshift stretchers being evacuated from the hospital.
Russian government spokesman Dmitry Peskov said the strikes were "pinpoint attacks" against "terrorists" prompted by the shooting down of its fighter jet.
"Naturally this tragic incident was followed by decisive actions in order to prevent terrorist activity," Peskov told CNN. "One thing is undeniable: it is an extreme concern that portable anti-aircraft missile systems are in the hands of terrorists. This is a huge danger for all states."
The Russian military has targeted a number of militant groups in Idlib, including al Qaeda's Syrian affiliate, Hayat Tahrir al-Sham, which has a strong presence in the province.
On Monday, the US accused Russia of blocking a UN Security Council statement condemning Sunday's alleged chemical attack. Russian UN Ambassador Vassily Nebenzia fired back, accusing the US and United Kingdom of "slandering" Russia and "spreading a mountain of lies" when it came to chemical weapons accusations.
US State Department spokeswoman Nauert reiterated the charge by Secretary of State Rex Tillerson that the "ultimate" responsibility for any chemical attacks by the Syrian regime lay with the Russian government.
"By shielding the Syrian regime from accountability, Russia has not lived up to its commitments," she said.
Airstrikes kill dozens in Ghouta
On Monday, dozens of airstrikes in the besieged Damascus suburb of Eastern Ghouta killed at least 29 people, including at least 6 children, according to SOHR.
Various Islamic rebel groups control Eastern Ghouta, and the enclave has been surrounded by Syrian regime forces for more than four years.
Both Eastern Ghouta and Idlib are considered part of the so-called "de-escalation zones" established in May 2017 as part of an agreement between Russia, Turkey and Iran.
Opposition condemns Russian 'war crimes'
The Syrian National Coalition said Monday that "strict measures need to be taken to put an immediate end to the war crimes and genocide Russia is committing in Syria."
The group, which was first formed in 2012 and comprises a number of different opposition factions, also called on Russia to end its support of Syrian President Bashar al-Assad, who it accused in the statement of "committing war crimes and crimes against humanity in Syria, including with the use of chemical weapons."
"A UN Security Council resolution is also urgently needed to ensure that the perpetrators of these crimes are held accountable, namely the Russian and Assad regimes and its allied foreign militias as well as those who have committed crimes against the Syrian people," the statement added.
'They brought hell to Idlib'
"In the last two days, shelling has intensified. It's manic and unprecedented. It's like they brought hell to Idlib," Raed Fares, one of the media activists CNN spoke to, said from his house in Kafranbil.
"They [Russian and Syrian forces] are targeting vital places: schools, hospitals, and the middle of towns and neighborhoods ... one cannot imagine the scale of destruction," Fares added.
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 over 1.1 million of Syria's 6.5 million internally displaced people (IDPs), 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.