Nine countries have demanded an urgent United Nations Security Council meeting on Monday after an alleged chemical attack on Syria's rebel-held town of Douma, diplomatic sources said on Sunday.
France initiated the move, and the request was also signed by the United States, Britain, Kuwait, Sweden, Poland, Peru, the Netherlands and Ivory Coast, the sources said.
The meeting is tentatively called for 1900 GMT on Monday but needs to be formally confirmed.
Along with Syria's ally Russia, France, the US and Britain are permanent members of the Security Council, as is China.
The other states which signed the request are non-permanent members of the body, which has met numerous times over the Syrian war since it began in 2011.
Foreign Minister Jean-Yves Le Drian said earlier Sunday that France will “do its duty” over the alleged chlorine gas attack against civilians in Syria's Eastern Ghouta region.
France has repeatedly warned that evidence of further use of chemical weapons in Syria was a “red line” that would prompt French strikes.
“The use of chemical weapons is a war crime,” Le Drian said in a statement.
Russian-backed regime forces launched a devastating assault in February to retake Eastern Ghouta, the last major opposition bastion close to Damascus.
Syria's White Helmets, who act as first responders in rebel-held areas of Syria, said an attack took place late on Saturday using “poisonous chlorine gas.”
In a joint statement with the Syrian American Medical Society (SAMS), the White Helmets said more than 500 cases were brought to medical centers “with symptoms indicative of exposure to a chemical agent.”
Moscow, which has continued to give the regime of Syria's President Bashar al-Assad diplomatic cover at the UN, on Sunday insisted that the Damascus regime had not used chemical weapons in Eastern Ghouta.
EU says 'evidence points' to chemical attack by Syria regime
The EU said on Sunday that evidence suggested the Syrian regime carried out a chemical attack in Douma and urged Damascus's allies Russia and Iran to help prevent another attack.
“The evidence points towards yet another chemical attack by the regime,” the European External Action Service said. “We call on the supporters of the regime, Russia, and Iran, to use their influence to prevent any further attack.”
Trump warns of 'big price'
Trump's threat came exactly a year and a day after the US fired cruise missiles at a Syrian airbase in retaliation for a deadly sarin gas attack in 2017.
“Many dead, including women and children, in mindless CHEMICAL attack in Syria,” Trump wrote on Twitter on Sunday, lashing out at Syrian President Bashar al-Assad and Russia's Vladimir Putin, a key ally of the regime.
“President Putin, Russia, and Iran are responsible for backing Animal Assad. Big price to pay,” he said.
Asked whether the US could again respond with a missile strike, White House homeland security adviser Tom Bossert told ABC television: “I wouldn't take anything off the table.”
The Russian foreign ministry called the latest reports a provocation and warned against them being used as a pretext for military action.
“A military intervention under far-fetched and fabricated pretexts in Syria, where there are Russian soldiers at the request of the legitimate Syrian government, is absolutely unacceptable and could have the most dire consequences,” it said in a statement.