Prime Minister-elect Tony Abbott believes there is every reason to be sceptical about Syrian leader Bashar al-Assad's sincerity about joining a chemical weapons ban.

But he hopes a diplomatic solution can be found.

US President Barack Obama has asked Congress to delay voting on US military action in Syria, arguing that Russia's plan to neutralise its ally's chemical weapons must be given a chance.

President Obama said in a televised speech that the Assad regime had admitted it had the weapons and "even said they'd join the chemical weapons convention, which prohibits their use".

Mr Abbott welcomed the speech but voiced some doubts about the regime's commitment.

"I welcome the president's announcement that - because of the credible threat of US military action against Syria - the Assad regime may be prepared to join the chemical weapons convention, which prohibits their use," Mr Abbott said in a statement on Wednesday.

"Given Assad's record, there is every reason to be sceptical about his sincerity.

"But Australia, including through our current role as president of the UN Security Council, will give every support to renewed United States efforts at finding a diplomatic solution that would mean Syria never again uses these terrible weapons."