"Chaos and extremism will spread" if the US and its Western allies decide to attack Syria, Assad said, adding "everyone will lose control of the situation once the powder keg explodes".
"The risk of a regional war exists," he said in an interview with French newspaper Le Figaro.
France should consider the consequences of its involvement in military action against Syria, he said. "There will be repercussions, negative ones of course, on the interests of France," Assad said.
Assad's remarks came as Washington and Paris are pushing for a military attack against Syria over the country's alleged use of poison gas against civilians, including an August 21 attack near Damascus the US says killed over 1,400 people.
Syria has repeatedly denied being behind the August 21 attack and accuses rebel fighters of using chemical weapons on government troops.
Meanwhile in Washington, hawkish senators John McCain and Lindsey Graham after holding talks with Obama said that they favoured passing a resolution to authorise for a military action against Syria.
"A vote against this would be catastrophic in its consequences, not only as far as this issue is concerned, but in the future," Republican Senator McCain told reporters.