Downing Street has said the Ministry of Defence is drawing up contingency plans for the use of military force against Syria.
On Tuesday morning a spokesperson for the prime minister said any response by the United Kingdom, United States and other members of the international community to the use of chemical weapons would be "something that is proportionate".
"From our own evidence and perspective it is clear that chemical weapons were used as they were used by the Assad regime. It is important when we see a crime of this sort, the use of chemical weapons against a regime's own people, there needs to be a response," the spokesperson said.
The spokesperson said that while "no decision has yet been taken" on the nature of the response it was "reasonable to assume our armed forces are making contingency plans" and that any action would be "taken within the framework of international law".
Asked what a "proportionate" response to the use of chemical weapons would be, Downing Street said this was "exactly what we are discussing".
No.10 also indicated action may be taken before the United Nations completes its report into the alleged use of chemical weapons in Damascus on August 21. The spokesperson said the UN investigation was a "parallel process" to the evidence that had been gathered by the British and American governments.
"It's possible that given the regime prevented that UN team from going in on day one the evidence on the site could have been tampered with," the spokesperson said.
"There is evidence that will come back from the UN so we will look at that, but there is still a parallel process going on that is the evidence we already have, the evidence that the Americans and other international partners have and there is a process of discussion which is going on at present between ourselves and our international partners."
An announcement will be made later today on whether David Cameron will recall parliament in order to give MPs a chance to discuss any potential strikes.
On Tuesday morning, Labour's shadow foreign secretary Douglas Alexander said MPs should be allowed to decide on any intervention and said if the government failed to convince the Commons, it would not have a "mandate in parliament" for action. He added: "I think that there should be a vote in parliament after the Government sets out its case."
A substantial number of Conservative MPs are opposed to intervening in the conflict and have long insisted they be given the chance to veto any military moves.
Andrew Bridgen told The Huffington Post UK on Monday evening that he suspected a "large proportion" of Tory MPs remained to be convinced by the arguments for starting another "shooting war in the Middle East".
"We are fortunate we live a parliamentary democracy, not a dictatorship. Parliament should be recalled," he said. "I think it's for the foreign secretary and the prime minister to come to the Despatch Box and persuade the House of the need [for intervention]."
Earlier this year the North West Leicestershire MP organised a letter signed by 81 other Tories urging Cameron to grant a vote before any action was taken.
In something of an understatement, Bridgen said given past assurances from the government that there would be a vote, the failure to hold one would provoke "consternation" among backbenchers.
His view was shared by Peterborough MP Stewart Jackson. The backbencher, who is also sceptical about the wisdom of intervention, told HuffPost UK: "I back a recall of parliament and there must be a debate and vote before any substantive UK involvement in the civil war."
Downing Street stopped short of promising there would be a vote on any military action - simply repeating the line that it was "important that parliament has its say".
The prime minister's spokesman also said that while on principle Cameron wanted to give parliament a chance to debate the issue "there may be a strategic need to take action quickly".
Cameron is due to chair a meeting of the National Security Council (NSC) on Wednesday to discuss potential responses to the deadly attack after breaking off his family holiday in Cornwall to return to Downing Street.
Nick Clegg has also cancelled a trip to Afghanistan to attend the meeting. A spokesman for Clegg said he supported the need for a "strong response" from the international community to the "abhorrent" use of chemical weapons.
On Monday evening US secretary of state John Kerry said evidence of the use of chemical weapons was already "real and compelling" and indicated further evidence would be unveiled soon.
In an emotive address that ratcheted up the rhetoric against Assad, Kerry laid the blame for the attack at the feet of the regime and said it was a "moral obscenity" that "should shock the conscience of the world".
Soon after, White House press secretary Jay Carney told reporters there was "very little doubt that the Syrian regime is responsible for this attack" and that Obama was "assessing a potential response".
As Washington and London raised expectations that military action would be taken, former prime minister Tony Blair urged the West to intervene in the Syrian civil war.
Writing in The Times the regime of Bashar al-Assad is launching an attack on civilians on a scale "not seen since the dark days of Saddam".
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