Syrian president Bashar al-Assad has not discounted the possibility of a US military attack even though threatened action was forestalled when he agreed to give up chemical weapons.

In an interview broadcast by Venezuela's state-run Telesur network on Wednesday, Assad said his government had confessions from rebels that they brought chemical weapons into Syria.

According to the broadcast's Spanish dubbing, Assad said all evidence pointed to rebel responsibility for the attack.

He said Syrian authorities had uncovered chemical arms caches and laboratories and that the evidence had been turned over to Russia, which brokered the deal that helped persuade US President Barack Obama to pull back from threatened military action over the gas attack on 21 August that killed civilians in a Damascus suburb.

In a speech at the United Nations on Tuesday, Obama said he would not use military force to depose Assad.

But Washington and Moscow remain at odds on how to hold Syria accountable if it does not live up to its pledge to dismantle its chemical weapons stockpile.

Assad predicted during the 40-minute interview that "terrorists" would try to block access of UN inspectors who entered Syria to secure the government's chemical arsenal.

Assad said he had evidence that countries including Saudi Arabia were arming Syrian rebels, but he had no proof that any particular country had supplied them with chemical weapons.

He was also asked about the apparent thaw in relations between the US and Iran, his government's chief patron in the region.

Assad called the development positive but said he did not consider it to mean that Tehran's leaders trusted Washington. He said it was important that the US stop pressuring Iran not to have nuclear technology.

Assad accused the Obama administration of lying to US citizens by claiming it had proof that Assad's government was responsible for the gas attack.