The members of the Security Council expect U.N. weapons inspectors to brief Secretary-General Ban Ki-moon shortly after they depart Syria on Saturday. Ban, in turn, will swiftly brief the Security Council on the findings, the diplomat said.
China, which along with Russia has staunchly opposed any military intervention in Syria, called for U.N. weapons inspectors to be allowed to complete their investigation.
"China calls on parties concerned to exercise restraints and calmness, adhering to the right track of political solution," Foreign Minister Wang Yi said in a statement.
Britain's Joint Intelligence Committee has concluded it was "highly likely" that Syrian government forces used poison gas outside Damascus last week in an attack that killed at least 350 people, according to a summary of the committee's findings released Thursday.
Speaking in the House of Commons before the vote, Cameron said failure to respond would undo "decades of painstaking work" to prevent such weapons from being unleashed.
"The global consensus against the use of chemical weapons will be fatally unraveled," he said. "A 100-year taboo will have been breached."
In Washington, White House spokesman Josh Earnest said Obama was still weighing a potential response, but said his administration was working on a "compressed timeline."
U.N. weapons inspectors are now in Syria trying to confirm the use of chemical weapons. The inspectors are expected to leave the country by Saturday morning, Secretary-General Ban Ki-moon said.
Syrian President Bashar al-Assad's government denies using the weapons against opposition forces and says its troops were the victims, not perpetrators, of recent gas attacks; but both British and U.S. officials say the rebels have no capability to use poison gas on the scale of the August 21 attack near Damascus, which opposition sources said killed more than 1,300.
"There is no credible intelligence or other evidence to substantiate the claims or the possession of CW by the opposition," Britain's Joint Intelligence Committee concluded in a document released Thursday. "The JIC has therefore concluded that there are no plausible alternative scenarios to regime responsibility."
Cameron said the debate was not about regime change or invasion. And he said his government would not act without first hearing from the U.N. inspectors, giving the world body a chance to weigh in and giving Parliament another chance to vote.
But the prime minister said failing to act would give al-Assad the unmistakable signal that he could use poison gas "with impunity." The British dossier on Syria also concluded the government had used chemical weapons on 14 previous occasions, and Cameron said al-Assad stepped up their use last week as a sort of test for the world.
The government said it could justify the use of force against Syria on humanitarian grounds, to stop the suffering, even if the United Nations declined to authorize a strike.
"The aim is to relieve humanitarian suffering by deterring or disrupting the further use of chemical weapons," the government said.
Syria's government offered its own arguments against such an intervention. In an open letter to British lawmakers, the speaker of Syria's parliament riffed on British literary hero William Shakespeare, saying: "If you bomb us, shall we not bleed?"
But in a veiled warning to the United Kingdom, the letter also invoked Iraq, a conflict justified on the grounds that Iraq had amassed stockpiles of chemical and biological weapons and was working toward a nuclear bomb -- claims that were discovered to have been false after the 2003 invasion.
"Those who want to send others to fight will talk in the Commons of the casualties in the Syrian conflict. But before you rush over the cliffs of war, would it not be wise to pause? Remember the thousands of British soldiers killed and maimed in Afghanistan and Iraq, not to mention the hundreds of thousands of Iraqi dead, both in the war and in the continuing chaos."
British Commons Speaker John Bercow published the letter. And al-Assad has vowed to defend his country against any outside attack.
"The threats of launching an aggression against Syria will increase its commitments to its rooted principles and its independent decision that originated from the will of its people, and Syria will defend itself against any aggression," the Syrian president said Thursday in a speech to Yemeni politicians.
Obama faces calls for American vote on force