The House of Commons will debate UK's response to the toxic gas attack in Syria on Thursday,
Mr Cameron has returned from his holiday
Prime Minister David Cameron has recalled Parliament for a debate and vote on the UK's response to Syria's toxic gas attack, which killed 1,300 people.
Mr Cameron, who is back in London after cutting short his family holiday, says a clear government motion will be put before MPs on Thursday.
He wrote on Twitter: "Speaker agrees my request to recall Parliament on Thurs. There'll be a clear Govt motion & vote on UK response to chemical weapons attacks."
Mr Cameron - who is holding a National Security Council (NSC) meeting on Wednesday - is under pressure to be able to legally justify any intervention.
While Britain's Armed Forces draws up plans for military action in Syria, the Assad regime says it will use "all available means" to defend itself.
A build-up of military aircraft at Britain's base on Cyprus, RAF Akrotiri, suggested that planning had reached a developed stage.
Foreign Secretary William Hague has declined to rule out action, such as targeted air strikes, being launched within days.
At the same time, Syrian Foreign Minister Walid Muallem says any foreign strike on his country would be "delusional".
He says Syria will defend itself against any strike using "all available means".
"We have two options: either to surrender, or to defend ourselves with the means at our disposal," he said.
"The second choice is the best: we will defend ourselves."
Mr Muallem also claims today's UN inspections had to be scrapped because of disputes between rebels.
Snipers shot at the UN team on Monday, but the inspectors still managed to collect some "valuable" samples.
The UN inspections will take place on Wednesday instead, Mr Muallem said.
US Secretary of State John Kerry has said the use of chemical weapons was "undeniable".
Syrian President Bashar Assad's would be held accountable, Mr Kerry said.
"Let me be clear. The indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity."
The US also postponed a Syrian crisis meeting with Russia that was scheduled for this week because of America's ongoing review of the attack.
Russia - the Syrian regime's most powerful ally - said postponing The Hague meeting was a "serious disappointment".
Moscow also warned that any use of force against Syria would have "catastrophic consequences".
"We call on our American colleagues and all members of the international community to show prudence, strict observance of international law, and above all, the fundamental principles of the UN Charter," the Russian Foreign Ministry said.
Russia's Emergencies Ministry has told Sky News that it is sending a plane to Syria today to take in humanitarian aid and is planning to bring around 150 of its citizens out.
Mr Assad denies using the chemical weapons and Moscow - which supplies arms to Syria - has backed claims that video footage of victims could be opposition propaganda.