Australians in Syria have been warned to leave the country immediately.

There are 59 Australians, including six children, registered as being in Syria, Foreign Minister Bob Carr said on Thursday.

He urged them to leave by road or air while it was still possible, ahead of an expected international response to last week's suspected chemical weapons attack in Damascus.

But they shouldn't use the Syria-Jordan crossing near the city of Der'a, the Tal Kalakh crossing into Lebanon, or any crossing into Iraq, he said.

A UN team is investigating last week's attack and will report back by the end of the week.

Meanwhile the US and its allies have been discussing possible military action against the Syrian regime.

"The risk of further violence is very high and there is no margin for safety in Damascus, Aleppo or any other city in Syria," Senator Carr said in a statement.

"Exit options are already limited and may be further reduced as airports and border crossings are closed.

"There are also no effective means of providing consular assistance, particularly outside Damascus."

Australians concerned about friends or relatives in Syria should contact the Consular Emergency Centre on 1300 555 135.