The two leaders agreed to stay in "close consultation" in the coming days as Mr Cameron prepared for a meeting of the National Security Council meeting today.
The Prime Minister has said any action in Syria would be to deter the future use of chemical weapons as he blamed a suspected poison gas attack on the Assad regime.
Mr Cameron said the scenes of death and suffering in Damascus were "appalling" and "we cannot let that stand".
Britain's Armed Forces are drawing up plans for a potential military intervention in response to the alleged chemical attack in the Syrian capital, which is believed to have killed hundreds of civilians.
Mr Cameron said any intervention had to be legal and proportionate and would not be about the Syrian conflict itself but preventing the use of chemical weapons by any regime.
And he stressed no decisions about UK involvement have been made.
He said: "Let me stress to people, this is not about getting involved in a Middle Eastern war or changing our stance in Syria, or going further into that conflict. It's about chemical weapons. Their use is wrong and the world should not stand idly by."
Parliament is being recalled and Mr Cameron, who is back in London after cutting short his family holiday, said a clear motion on the crisis would be put before MPs on Thursday.
Deputy Prime Minister Nick Clegg said Britain will not engage in an "open-ended military" conflict and "we're not considering regime change".
Foreign Secretary William Hague has declined to rule out action, such as targeted air strikes, being launched within days, and the PM is under pressure to be able to legally justify any intervention.
He spoke to US President Barack Obama on Tuesday night but a Downing Street spokeswoman said there would be no decision on what action to take ahead of a National Security Council meeting Mr Cameron will hold on Wednesday.
A build-up of military aircraft at Britain's base on Cyprus, RAF Akrotiri, suggested that planning had reached a developed stage.
But a YouGov poll for the Sun newspaper claimed 50% of people questioned said they opposed a military strike against Syria, with only 25% in favour.
It comes as the US defence secretary Chuck Hagel said his country was "ready to go" if Mr Obama orders action.
Mr Hagel said the president asked the Pentagon to give him "all options for all contingencies".
"We are prepared. We have moved assets in place to be able to fulfil and comply with whatever option the president wishes to take," he told the BBC.
US Vice-President Joe Biden said there was no question that Syria's President Bashar Assad was responsible for the attack - the highest-ranking US official to say so.
And the White House dismissed as "fanciful" the notion that anyone other than Mr Assad could be to blame.
"Suggestions that there's any doubt about who's responsible for this are as preposterous as a suggestion that the attack did not occur," spokesman Jay Carney said.
He also said the options the White House was considering were not about regime change.
Rebels in Syria have handed Western powers a list of suggested targets for a strike, according to a Reuters source.
France's President Francois Hollande said his country was prepared to "punish" those who gassed innocent people last Wednesday and it seemed certain that forces loyal to Mr Assad were behind the attack.
Sky's Foreign Affairs Editor Tim Marshall said any potential action "would be a punch on the nose for the Assad regime. I don't think the US is ready for Assad to go because they are frightened of who would take his place."
But Syria insists it will not submit quietly to an attack.
"We have two options: either to surrender, or to defend ourselves with the means at our disposal. The second choice is the best: we will defend ourselves," said Syrian foreign minister Walid Muallem.
He also claimed Tuesday's UN inspections of alleged chemical attack sites 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.
Syria denies using the chemical weapons and Russia - which supplies arms to Syria and is the regime's most powerful ally - has backed claims that video footage of victims could be opposition propaganda.
"I challenge those who accuse our forces of using these weapons to come forward with the evidence," Mr Muallem said.
The Arab League has accused the Syrian regime of carrying out the suspected gas attack and Saudi Arabia has called for "firm and serious" action against the state.
But Moscow has 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.
And deputy prime minister Dmitry Rogozin claimed western countries were behaving in the Islamic world like a "monkey with a grenade".
It is unclear whether Mr Obama would seek authority from the UN or Congress before using force. But it is likely Russia and China would block US efforts to authorise action through the UN Security Council.