Syrian President Bashar Assad, during an interview that aired Monday morning, threatened "repercussions" from any American attack on Syria.
The Syrian leader, speaking with CBS News, said the U.S. can expect "every action" if America strikes. He suggested retaliation could come from the opposition, as well as his own government and its allies.
"You should expect everything," Assad said. Asked to elaborate, he added: "You should expect everything. Not necessarily from the government. ... You have different parties, you have different factions, you have different ideology."
Asked specifically if the attack could trigger more chemical warfare, Assad suggested the rebels would be the ones who would use them. He said that outcome depends on whether "terrorist" rebels possess those weapons, adding: "It could happen."
Assad used the interview to challenge the Obama administration's claims that his regime used chemical weapons in an attack that killed hundreds on Aug. 21. He said his soldiers were "in another area" at the time of the attack.
It comes as President Obama prepares to deliver a national address on Tuesday making his case for a military strike on Syria. The matter is currently before Congress, which will begin a set of votes this week on a resolution authorizing the use of force.
Obama on Monday also planned to make his case, in a string of interviews, for punishing Assad.
Top administration officials are heading to Capitol Hill for more classified briefings. And White House national security adviser Susan Rice is scheduled for a speech at a Washington think tank timed to the public relations blitz aimed at ensuring people the administration isn't contemplating another commitment like Iraq and Afghanistan.
In an interview Sunday in Damascus, Assad told American journalist Charlie Rose there is no conclusive evidence about who is to blame for the chemical weapons attacks and again suggested the rebels were responsible. Rose said Assad also warned him previous U.S. military efforts in the region have proved disastrous.
And Assad argued the evidence Secretary of State John Kerry has disclosed amounts to a "big lie" that resembles the case for war in Iraq that Secretary of State Colin Powell made to the United Nations over a decade ago.
Appearing Monday at a news conference in London with British Foreign Secretary William Hague, Kerry said of Assad: "What does he offer? Words that are contradicted by fact."
"We know that his regime gave orders to prepare for a chemical attack. We know they deployed forces," the secretary said. He added that the United States knows "where the rockets came from and where they landed ... and it was no accident that they all came from regime-controlled territory and all landed" in opposition-held territory.
"So the evidence is powerful and the question for all of us is: What are we going to do about it? Turn our backs? Have a moment of silence?"
He said that if Assad wanted to defuse the crisis, "he could turn every single bit of his chemical weapons over to the international community" within a week. But he said that Assad "isn't about to do it."
The Associated Press contributed to this report.