Britain has led renewed calls for diplomatic action over the use of chemical weapons against civilians in Syria as the US appeared to toughen its stance against Bashar Assad.
The US, UK and France have brought a resolution before the United Nations Security Council demanding an investigation into the suspected chemical attack, which is believed to have killed at least 72 people, including 20 children.
Foreign Secretary Boris Johnson said no one could reasonably object to the UN resolution, while Downing Street had previously played down the prospect of military action.
However, late on Thursday, US president Donald Trump was reported to be seriously considering military action in response to the attack.
US defence secretary James Mattis was said to be preparing to brief President Trump on military options, while secretary of state Rex Tillerson criticised the attacks in Syria as a "serious matter that requires a serious response".
Speaking aboard Air Force One, Mr Trump said what happened in Syria was "a disgrace to humanity".
Asked if President Assad should go, Mr Trump said: "He's there and I guess he's running things, so something should happen."
The president would not discuss what, if anything, the US might do in response to the deadly chemical attack.
He said the attack "shouldn't have happened, and it shouldn't be allowed to happen".
Speaking at a press conference, Mr Johnson said no one could reasonably object to the UN resolution.
"We in the UK, together with our French friends, have called an emergency meeting of the UN Security Council," he said.
"We have tabled a resolution which I hope absolutely everybody feels able to sign up to.
"Because all we are saying is that there should be condemnation of that chemical weapons attack, and secondly, that there should be a thorough and urgent international investigation, and I don't think anybody could possibly, reasonably, oppose such a resolution."
On Wednesday, Downing Street played down the prospect of military action in retaliation for the use of chemical weapons against civilians, insisting "nobody is talking" about an armed response to the atrocity.
The draft resolution backs an investigation by the Organisation for the Prohibition of Chemical Weapons and demands the Syrian government provides information about its military operations on the day of the strike.
The text calls on Syria to provide flight plans, flight logs and other information on its military operations on April 4 and to hand over the names of commanders of helicopter squadrons.
A vote on the resolution was delayed beyond Thursday, with consultation ongoing among council members.
Russia is expected to veto the UN resolution, though, having previously used its veto power seven times to block UN action that would put pressure on its ally Syria.
Russia's defence ministry said the toxic agents were released when a Syrian air strike hit a rebel chemical weapons arsenal and munitions factory.
But Mr Johnson said he had seen "absolutely nothing to suggest" the attack was carried out by anyone but the government of Syria.