Military commanders from Western and Muslim countries are meeting in Jordan to discuss the Syria conflict, as Western powers weigh military action in response to a suspected chemical weapons attack.

The meeting, which was expected to start late on Sunday, came at the invitation of Jordan's chief of staff Meshaal Mohamed al-Zaban and General Lloyd Austin, head of Centcom, the US command responsible for 20 countries in the Middle East and Central Asia, according to Jordanian officials.

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America's top military officer General Martin Dempsey was taking part, as well as chiefs of staff from Saudi Arabia, Qatar, Turkey, Britain, France, Germany, Italy and Canada, said an official cited by Jordan's state news agency.

Syria agreed on Sunday to let the United Nations inspect the site of the alleged chemical weapons attack, but a US official told Reuters news agency that such an offer was "too late to be credible" and Washington was all but certain that the government of President Bashar al-Assad had gassed its own people.

The comments follow forceful remarks from other Western powers, including Britain and France, which also said they believe Assad's government was behind the massive attack that killed many hundreds of people last week.

Earlier on Sunday, US Defence Secretary Chuck Hagel said the US military was ready to take action against the Syrian government if ordered.

Jordanian Foreign Minister Nasser Judeh said the meeting had been scheduled for months.

"The meeting is not a reaction to what happened recently in Syria. It is one of a series of meetings of the army chiefs of countries concerned about the situation in Syria," he added.

"At the same time, the meeting will discuss the situation and scenarios on the ground, especially after the recent dangerous developments. The army chiefs have to have comprehensive talks and examine the impact on the region."

Syria's information minister has said any US military action would "create a ball of fire that will inflame the Middle East".