Syrian President Bashar al-Assad warned Washington on Monday to brace for retaliation if US forces attacked his war-torn country, as he denied using chemical weapons against his people.

"You're going to pay the price if you're not wise. There are going to be repercussions," Assad told CBS television's "This Morning."

"It's an area where everything is on the brink of explosion. You have to expect everything."

He also warned of the risks of possible chemical attacks by rebels or "terrorists" if there was outside intervention in Syria.

Assad spoke in what CBS called his first interview since President Barack Obama asked Congress for approval to use military force to punish Assad for his regime's alleged use of chemical weapons in a deadly attack last month.

"You should expect everything... The government's not the only player in this region. You have different parties, different factions, different ideologies. You have everything in this decision now," Assad said.

Assad denied his forces carried out a deadly chemical weapons attack on August 21 on the outskirts of Damascus, as alleged by the United States and some of its allies.

"How can you talk about what happened if you don't have evidence?" he said in the interview, in which he spoke English.

"We're not like the American administration, we're not like the social media administration or government. We're the government that deals with evidence."

Assad said that his forces had themselves in fact been attacked by rebels using chemical arms.

"But in the area where they say the government used chemical weapons, we only have video and we only have pictures and allegations. We're not there. Our forces, our police, our institutions don't think this," Assad said.

Asked whether the repercussions he predicted could include the use of more chemical weapons, Assad replied: "That depends. If the rebels or the terrorists in this region or any other group have it, it could happen. I don't know. I'm not a fortune teller to tell you what's going to happen."

US President Barack Obama will on Tuesday address Americans from the White House to discuss intervention in Syria, ahead of a possible Senate vote on authorizing force against Assad's regime later this week.

US Secretary of State John Kerry, who testified before a the Senate Foreign Relations Committee last week seeking its support for military action, said Monday that Assad could avert an attack by giving up his chemical weapons.

But Kerry said he had no expectation Assad would do this.