Speaking in an interview with Russia Today television, Mr Assad said he did not see the West embarking on a military intervention in Syria and said the cost of such action would be unbearable.
"I think the cost of a foreign invasion of Syria – if it happens – would be bigger than the entire world can bear. This will have a domino effect that will affect the world from the Atlantic to the Pacific," he said.
It was not clear when President Assad gave the interview.
His defiant remarks coincided with a landmark meeting in Qatar yesterday of Syria's fractious opposition to hammer out an agreement on a new umbrella body uniting rebel groups inside and outside Syria amid growing international pressure to put their house in order and prepare for a post-Assad transition.
The US and other Western powers are frustrated with the opposition over divisions and in-fighting which have undermined the chances of ousting Mr Assad.
Backed by Washington, the Doha talks underline Qatar's central role in the effort to end President Assad's rule as the Gulf state, which funded the Libyan revolt to oust Muammar Gaddafi, tries to position itself as a player in a post-Assad Syria.
"I am tougher than Gaddafi," Mr Assad told his interviewer, according to a tweet posted by the editor-in-chief of the station.
The President, who is battling to put down a 19-month old uprising against his rule, said he would "live and die in Syria", in what appeared to be a rejection of the idea by British Prime Minister David Cameron this week a safe exit and foreign exile could be one way to end the civil war in Syria.
"I am not a puppet and the West did not manufacture me in order that I leave to the West or any other country. I am Syrian, I am Syrian-made, and I must live and die in Syria," he said.
Opposition groups estimate 38,000 people have been killed in the war.
International and regional rivalries have complicated efforts to mediate a resolution to the conflict. Russia and China have vetoed three UN Security Council resolutions.
Foreign Minister William Hague said Britain will now talk directly to Syrian fighters inside the country.