Pressure grows on British Prime Minister David Cameron to recall Parliament
David Cameron will respond to mounting demands by MPs to recall Parliament to discuss Syria as Britain and international allies contemplate launching military action over the use of chemical weapons.
The Prime Minister has returned early to Downing Street from a family holiday to prepare for a national security council (NSC) meeting tomorrow which will discuss possible UK involvement in using force against the Assad regime.
America significantly toughened its rhetoric over what it described as the "undeniable" use of banned nerve agents by the Syrian government against an opposition-held suburb of the capital Damascus.
US secretary of state John Kerry said the attack, which doctors say killed hundreds, was a "moral obscenity" that "should shock the conscience of the world" and promised action to hold the regime accountable.
The mood darkened further when United Nations weapons inspectors investigating the claims came under sniper fire as they drove to the area despite assurances of their safety from both sides in the civil war.
As he continued a round of diplomatic calls with world leaders, Mr Cameron clashed with Vladimir Putin over Russia's continued insistence that there is "no evidence" of a chemical attack.
Assad denies using the weapons and Moscow - a key regime ally which supplies arms to Syria - has backed claims video footage of victims could be opposition propaganda.
It says military action would be a violation of international law and doomed to fail.
The Prime Minister told Mr Putin there was "little doubt" the regime had used the weapons and then acted to cover up the evidence for five days before allowing the inspectors in, showing it had "something to hide".
Foreign Secretary William Hague suggested force could be legal even if Russia vetoed UN Security Council backing and declined to rule out action, such as targeted air strikes, being launched within days.
Any intervention would be "in accordance with international law and will be based on legal advice to the national security council and to the Cabinet", Mr Hague stressed.
Deputy Prime Minister Nick Clegg has cancelled a visit to UK troops serving in Afghanistan so that he can attend the NSC meeting.
A spokesman for Mr Clegg said he supported the need for a "strong response" from the international community to the "abhorrent" use of chemical weapons.
The party leaders face significant opposition to British involvement in military action - which may be exposed if Downing Street, as expected, decides to accept cross-party calls for Parliament to be recalled.
MPs are due back from their summer break next Monday but Labour and a growing number of backbench MPs from all parties - including many Tories - are demanding a chance to debate the situation more quickly.
Shadow foreign secretary Douglas Alexander said the Prime Minister should "make his case to Parliament" before any action was taken.
"While of course I understand the Foreign Secretary's reluctance to discuss specific military deployments, he and the Prime Minister do need to be open about the objectives, the legal basis, and the anticipated effect of any possible UK military action in Syria," he said.
Tory MP Sarah Wollaston said there was no threat to UK national security and Parliament should be consulted to act as a brake to any "headlong rush" into an escalation of the situation.
The chairs of several influential Commons committees also joined forces to table a Commons motion calling for a recall.
A Downing Street spokesman said the Government would decide "whether the timetable for our response means it will be necessary to recall MPs sooner than Monday when the House is currently due to return".
Former Liberal Democrat leader Sir Menzies Campbell said it was "inconceivable" to act before the UN inspectors had completed their work and that MPs' prior approval should be sought in a Commons vote unless the Prime Minister had a "very good reason" not to wait for it.
Sir Menzies said the situation was different from that of Libya - when Parliament met only after action was taken - because in that case there was United Nations backing for humanitarian intervention.
One Tory MP who has been vocal in opposing Western military involvement in Syria indicated that he could accept the need for a "surgical military punishment strike" as a message to the regime that chemical weapon use would not be tolerated.
Julian Lewis told the Guardian: "If we can be satisfied that the Syrian government has carried out this atrocity using sarin gas there is an argument to be made for some sort of surgical military punishment strike to show the regime that such behaviour will not be tolerated in the 21st century."
He compared it with the 1986 air strikes against Libya which had changed the behaviour of Muammar Gaddafi.
In an uncompromising statement Mr Kerry said evidence of the use of chemical weapons was already "real and compelling" but that "additional information" would be made available in the coming days.
In a clear message to Moscow, he said anyone who continued to claim doubts about the footage of the aftermath of the attack "needs to check their conscience and their own moral compass".
And though he gave no details of what the response might be, he said Mr Obama "believes there must be accountability for those who would use the world's most heinous weapons against the world's most vulnerable people".
"By any standard it is inexcusable and despite the excuses and equivocations that some have manufactured, it is undeniable," he said.
"No matter what you believe about Syria, all peoples and all nations who believe in the cause of our common humanity must stand up to ensure that there is accountability for the use of chemical weapons so that it never happens again.
"Anyone who can claim that an attack of this staggering scale could be contrived or fabricated needs to check their conscience and their own moral compass."
The US State department has postponed a meeting with Russian diplomats on Syria that was scheduled for this week because of America's ongoing review into alleged use of chemical weapons.
The meeting, at The Hague, was to set up an international conference to find a political resolution to the Syrian crisis.
Mr Alexander said the Government must give answers to key questions.
Speaking on BBC Breakfast, he said: "The right response is not simply to say something must be done, however loudly. It is to both ask and answer the question 'What steps can be taken to make a horrendous situation better?'
"Now, as the Labour Party, we have never in principle ruled out the use of force in Syria. But we haven't yet heard from the Government what its strategic objective would be for any military action.
"Would it be to degrade and diminish the capability of Assad to use chemical weapons? Would it be an attempt to try and change the course of a highly complex, intractable civil war?
"We simply haven't had those questions answered.
"And that's why I do think the Prime Minister should bring Parliament back so that they can offer their case both to politicians and to the people before any decision is taken to commit British forces into combat."