The US Defence Secretary has said that his country and its allies are still trying to figure out details of Syria's suspected use of chemical weapons against its own people.

"We are continuing to assess what happened - when, where," said Chuck Hagel on Monday.

"I think we should wait to get the facts before we make any judgments on what action, if any, should be taken, and what kind of action."

Speaking to Pentagon reporters, Hagel refused to discuss any military options including whether or not the US would be willing to take unilateral action against the Syrian regime or if the administration would act only in concert with allies.

The administration of Barack Obama, the US president, said last week that US intelligence had concluded that Syrian government forces likely used chemical agents against rebels in two attacks, but said there were "varying degrees of confidence" about how large an attack it may have been.

Attack sites

US officials, including Secretary of State John Kerry, have said that chemical weapons - likely the nerve agent sarin - were used on two occasions.

Since then the administration has come under withering criticism from members of Congress demanding that the US take steps to protect the Syrian people by setting up either a safe zone or a no-fly zone over at least parts of the country.

International officials are pressing for broader access to suspected attack sites.

Syria, however, wants any investigation limited to an incident in the Khan al-Assal village in the Aleppo province in March that reportedly killed 31 people. However, Ban Ki-moon, the UN secretary general, wants a broader investigation that would include a December incident in Homs.

Obama has said that use of chemical weapons by President Bashar Assad's regime, or the transfer of those stockpiles to "terrorists" would cross a "red line" and have "enormous consequences".

Source: Agencies