Obama insists Syria behind chemical weapons attack

US President Barack Obama says that the US has "concluded" that the Syrian government carried out a deadly chemical weapons attack on civilians in a Damascus suburb last week. 

But in Wednesday's interview with Public Broadcasting Service (PBS), he said he had not yet made a decision about whether to intervene militarily.

Obama did however say that any strike against Syria would be to "send a shot across the bow" to deter future chemical weapons attacks.

Obama did not present any direct evidence to back up his assertion that the Syrian government bears responsibility for the alleged attack.

While he said he is still evaluating possible military retaliation, the president vowed that any American response would send a "strong signal" to Syrian President Bashar al-Assad.

"We have concluded that the Syrian government in fact carried these out," Obama said during the interview with PBS' NewsHour. "And if that's so, then there need to be international consequences."

"If we are saying in a clear and decisive but very limited way, we send a shot across the bow saying, stop doing this, this can have a positive impact on our national security over the long term," the president said in the televised interview.

But new hurdles emerged that appeared to slow the formation of an international coalition that could use military force to punish Syria.

Earlier on Wednesday, the five permanent members of the United Nations Security Council failed to reach an agreement on a draft resolution from the British seeking authorisation for the use of force.

Russia, as expected, objected to international intervention.

Obama administration officials said they would take action against the Syrian government even without the backing of allies or the United Nations, because diplomatic paralysis must not prevent a response to the alleged chemical weapons attack outside the Syrian capital last week.

Despite the administration's assertions that it would press forward without the UN, momentum for international military action appeared to slow.

British Prime Minister David Cameron promised British lawmakers he would not go to war until a UN chemical weapons team on the ground in Syria has a chance to report its findings, pushing the UK's involvement in any potential strike until next week at the earliest.

Cameron called an emergency meeting of parliament on Thursday to vote on whether to endorse international action against Syria.

Obama said he was not seeking a lengthy, open-ended conflict in Syria, indicating that any US response would be limited in scope.

But he argued that Syria's use of chemical weapons not only violated international norms, but threatened "America's core self-interest".

"We do have to make sure that when countries break international norms on weapons like chemical weapons that could threaten us, that they are held accountable," he said.