Rudd says Obama mulling 'full range' of options on Syria

Australia assumes the rotating presidency of the UN Security Council next month and Rudd spoke to Obama Tuesday to "chart a way forward" after an apparent chemical weapons attack left hundreds dead.

Rudd said it was becoming increasingly clear that the regime of Bashar al-Assad carried out last week's strike on a civilian community near Damascus.

"The international community is increasingly concluding that chemical weapons were used and that the Assad regime, in all probability, was responsible," said Rudd.

"This will be a crime against humanity and a violation of international law. It will not be without consequence. President Obama is considering options."

Rudd added that he expected UN inspectors, who braved sniper fire to gather evidence on Monday, to "fortify the conclusions which are emerging across the international community".

"You've got to ask yourself some basic questions as we look at final conclusions on this," he said.

"Who possesses chemical weapons in Syria? Answer, the regime. Who possesses the delivery systems capable of launching chemical weapons in the targets in which they were launched? Answer, the regime."

He added that history would judge the response by the international community, warning that it "cannot turn a blind eye".

"He (Obama) is focused on the full range of options which he is in the process of discussing with his partners and allies around the world," said Rudd, a former foreign minister who faces national elections in Australia on September 7.

"I, like the president of the United States, am driven by a core imperative here, which is not allowing a message to be conveyed to the international community that the use of chemical weapons against anybody in the year 2013 is acceptable under any circumstances.

"That is critical beyond Syria, it is critical for all decent people across the world."