Syria set a presidential election for June 3 on Monday, preparing the ground for leader Bashar Al-Assad to defy widespread opposition and extend his grip on power days after he said the war was turning in his favour.

The three-year-old rebellion against Assad's rule has killed more than 150,000 people, forced millions to flee their homes and seen the government lose control over swathes of territory. Hundreds more died on Sunday and Monday.

A leading Syrian opposition group said on Monday the election showed the president was divorced from reality.

Western and Gulf countries that back Assad's opponents had called plans for the vote a "parody of democracy" and said it would wreck efforts to negotiate a peace settlement.

United Nations-backed talks in Geneva collapsed in February with both sides far from agreement - not least over the question of whether Assad should go. No date has been set for their resumption.

Monzer Akbik, chief of staff of the president's office of the main Western-backed National Coalition opposition group, told Reuters the election was a sign Assad was unwilling to cooperate on finding a political solution to the conflict.

"This is a state of separation from reality, a state of denial. He didn't have any legitimacy before this theatrical election and he will not after," he said.

"We do not know what actor he is putting up as an opponent but we are not taking this seriously."

Infighting has fragmented the anti-Assad forces during the conflict, and several major opposition figures have not attended the Geneva talks.

Assad has not said whether he will stand again, but his allies in Russia and in Lebanon's Shi'ite movement Hezbollah have predicted he will participate and win.

In state-controlled parts of the capital Damascus, preparations for his candidacy have already begun. - Reuters