Assad said the main aim of a Russian-backed regime offensive in Aleppo province that has prompted tens of thousands of people to flee was to cut the rebels' supply route from Turkey.

He said his government's eventual goal was to retake all of the country, large swathes of which are controlled by rebel forces or the Islamic State (IS) jihadist group.

"It makes no sense for us to say that we will give up any part," he said in the interview conducted on Thursday in Damascus, before a plan for a nationwide "cessation of hostilities" in Syria was announced.

Assad said it would be possible to "put an end to this problem in less than a year" if opposition supply routes from Turkey, Jordan and Iraq were severed.

But if not, he said, "the solution will take a long time and will incur a heavy price". Assad said he saw a risk that Turkey and Saudi Arabia, key backers of the opposition, would intervene militarily in Syria.     

World powers yesterday announced an ambitious plan to stop fighting in Syria within a week, but doubts have emerged over its viability, especially because it did not include IS or Al-Qaeda's local branch.

US Secretary of State John Kerry said there were 'no illusions' about the difficulty of implementing a nationwide 'cessation of hostilities' as he announced the deal in Munich alongside Russian Foreign Minister Sergei Lavrov.

The US State Department also hit back at Assad's claim he wants to retake the whole country, with spokesman Mark Toner calling him "deluded if he thinks that there's a military solution to the conflict".

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