Britain would consider joining US military strikes against the Syrian government if there is evidence chemical weapons are being used against civilians, Foreign Secretary Boris Johnson said on Tuesday.
Johnson said he hoped Britain and other Western nations would not stand by in the event of a chemical attack, voicing support for limited strikes if there is "incontrovertible evidence" of the Syrian's government involvement.
"If we know that it has happened, and we can demonstrate it, and if there is a proposal for action where the UK could be useful then I think we should seriously consider it," Johnson told BBC radio.
Over the past week, Syria's army and its allies have subjected the rebel-held enclave of Ghouta near Damascus to one of the heaviest bombardments of the seven-year war, killing hundreds.
Britain is part of the US-led coalition involved in air attacks on Islamic State in Syria and Iraq, but the government lost a parliamentary vote on the use of force against the Syrian government in 2013.
Johnson said he supported the US decision to fire cruise missile at Syrian government targets last year after almost 100 people, including children, were killed in a gas attack on the opposition-held town of Khan Sheikhoun.
The United Nations accused the Syrian government of being responsible for an attack that used sarin gas.
"What we need to ask ourselves as a country and what we in the West need to ask ourselves, is can we allow the use of chemical weapons, the use of these illegal weapons to go unreproved, unchecked, unpunished," Johnson said.
However, he warned there was little international appetite for sustained military action against the Syrian regime.
"The people listening to us and this program in eastern Ghouta cannot get the idea the West is going to intervene to change the odds dramatically in their favour," he said.
The Syrian government has repeatedly denied using chemical weapons and said it targets only armed rebels and militants.