As MPs prepare to vote on whether Britain should join its allies launching airstrikes in Syria, the country's president accused them of "supporting terrorists".
But he praised military action by his ally Russia, which has been accused of targeting moderate rebels as well as jihadists.
Mr Assad said: "Since the beginning of that (US-led) coalition, if you want to talk about facts, not opinion, since the beginning of that coalition, ISIS (Islamic State group) has expanded and the recruiting from around the world has increased.
"While since the participation of Russia in the same fight, so-called against terrorism, ISIS has been shrinking. And al-Nusra (Nusra Front) of course and the other terrorist groups. So this is reality. The facts are telling."
Asked what it would take to end Syria's four-year civil war, which has killed more than 200,000 people, Mr Assad said: "When those countries that I mentioned - France, UK, US, Saudi Arabia, Qatar and some other - stop supporting those terrorists.
"(the next) day the situation will be better and in a few months we will have full peace in Syria, definitely. If they stop."
The US, UK, and other Western powers fighting Islamic State have demanded that Mr Assad steps down and have backed rebel groups fighting his forces.
Meanwhile the Syrian president has referred to all his opponents as "terrorists" and accused world leaders pushing for his departure of "supporting terrorists".
The Syrian leader is backed by Russia and Iran and he praised Vladimir Putin for launching a bombing campaign backing Assad's forces in September.
In a wide-ranging interview with Czech TV, Mr Assad also said:
"The feeling is very sad. Especially if you think about every person of those Syrians who left Syria has sad story behind him.
"It reflects the hardship of the Syrians during the crisis. From this (rational) way of looking at the situation, it's a loss.
"Every one of those is a human resources that left Syria. So that will undermine. Undermine your society and your country. Definitely. But at the end we have to deal with the reasons."
:: On Turkey Downing A Russian Jet:
"I think it has shown the real intention of Erodgan (Turkish President, Recep Tayyip Erdogan) who, let's say, lost his nerve because the Russian intervention has changed the balance on the ground.
"So the failure of Erdogan in Syria, the failure of his terrorist groups means his political demise."
:: On Relations With The West:
"If you look at the relation with the West, in 2005 I was the killer. In 2008 and after I was a peacemaker.
"Then in 2011 I became the vulture. Now, there's some positive change - of course shy kind of change, not the explicit one."
:: On Stepping Down:
"Now in the middle of the war, I'm not going to say I'm leaving for any reason," he said.
"When there's election, the Syrian people will decide if they want me, I'll be happy to be president, if they don't want me, I'll be happy to leave it, I don't have any problem."
:: On France's Effort To Broaden The Anti-IS Coalition:
"If they wanted to learn from what happened in Paris recently, why didn't they learn from Charlie Hebdo (attack)? The same principle, the same concept.
"And we said at that time that this is only the tip of the iceberg. What's under the water is much bigger. They didn't learn."
