Defence Secretary Philip Hammond has said that anyone found to be responsible for an alleged chemical attack in Damascus "should be in doubt that they will be held to account".
He said Britain is pushing with the "utmost urgency" for UN inspectors to be given access to the sites to make an "objective assessment".
Sweden's foreign minister Carl Bildt has said he believes Syrian forces are to blame for the alleged chemical attack, based on the evidence he has seen.
Writing in Swedish on his official blog, Mr Bildt said:
– carl bildt, swedish foreign minister
I have a hard time coming to any conclusion other than that a deadly chemical substance has been used in the attack carried out by the regime's forces between Tuesday and Wednesday on this opposition-controlled area.
He also said that if such an attack was confirmed by UN inspectors, he believes it would force Russia to reconsider its position and perhaps result in stronger action by the UN Security Council.
US President Barack Obama has described allegations of a chemical attack in Syria as a "big event of grave concern" and said that it would be "very troublesome" if they were verified.
He told CNN's 'New Day' programme that he does no expect the Syrian regime of President Bashar al-Assad to cooperate, based on previous experience.
Asked about the so-called "red line" that he previously said a chemical attack would represent, he admitted he still had to look at the latest event in detail.
With UN weapons inspectors still refused access into Syria by the Assad regime, it is not yet clear what actually caused so many deaths in Damascus.
Most experts say it looks like some kind of chemical attack took place, but there is disagreement whether a nerve agent like Sarin is to blame.
The chemical evidence will remain for only another 12 to 24 hours, which means time to establish the facts of what happened is running out, as Paul Davies reports.
Warning: This report contains graphic images
The US State Department said that at this time "we are unable to conclusively determine chemical weapons use" in Syria following reports of an attack.
Spokesperson Psaki: We have been unable to conclusively determine chemical weapons use, are working urgently to gather information. #Syria
State Department spokeswoman Jen Psaki said that if the reports of an attack were true, "It would be an outrageous and flagrant escalation" of the use of chemical weapons by Bashar al-Assad's government.
Damascus is the "chemical weapons capital of Syria" and contains a "network of jealously protected weapons facilities," according to research by Channel 4 News.
Based on thousands of videos and social media updates, Channel 4 also reports that rebel groups have accused the government of 30 separate chemical attacks. The government has reportedly made only one such accusation.