United Nations: The UN Security Council will hold emergency talks on Wednesday after a suspected chemical attack in Syria left over 50 dead and many wounded, a media report said.
The attack on a rebel-held town brought furious international reaction, with the US and other powers blaming the Syrian government for the deaths, the BBC reported.
Officials in Damascus, however, denied using any such weapons.
The attack will overshadow a conference in the Belgian capital Brussels at which 70 donor nations will discuss aid efforts in Syria, the BBC report said.
Delegates want to step up humanitarian access for thousands of civilians trapped by fighting.
The Syrian Civil War has raged for more than six years with still no political solution in sight.
Nearly five million Syrians have fled the country and more than six million are internally displaced, the UN said. More than 250,000 people have been killed.
Wednesday's emergency meeting of the UN Security Council was called by France and the UK as international outrage mounted over the suspected gas attack on Khan Sheikhoun in Idlib province on Tuesday.
Britain's Ambassador to the UN, Matthew Rycroft, described it as "very bad news for peace in Syria", the BBC said.
"This is clearly a war crime and I call on the Security Council members who have previously used their vetoes to defend the indefensible to change their course," he told reporters in New York.
Footage from the scene showed civilians, many of them children, choking and foaming at the mouth.
Witnesses said clinics treating the injured were then targeted by air strikes.
UK-based monitoring group the Syrian Observatory for Human Rights put the death toll at 58, including 11 children.
It was unable to say what chemical was dropped but pro-opposition groups said it was believed to be the nerve agent Sarin.