The Syrian opposition said it rejected any attempt by the government to delay the next round of peace talks until after a parliamentary election on April 13 and urged Russia to press its ally into serious talks on a political transition.

Syrian President Bashar al-Assad called the election last month, in a sign of confidence reflecting his growing momentum on the battlefield after five years of civil war. Elections are held every four years and the last one was in 2012.

The two warring sides have been holding separate talks for the past week in Geneva with U.N. Special Envoy Staffan de Mistura, who has said he plans to suspend them on Thursday and resume in early April.

"We're aware that the regime has asked for a two-week delay for the next round of talks. The regime is trying to evade its responsibilities and postpone negotiations," Yahya Qadamani, deputy coordinator of the opposition High Negotiations Committee (HNC), told a news conference in Geneva.

"We insist that the next round be held on time. The regime is not entitled to impose any postponement of the next round that begins on the April 4."

"We hope that Russia uses its influence on the Assad regime to enter into serious negotiations over a political transition," he said, making clear also that the political transition should end with the ousting of Assad.

Earlier, HNC spokesman, Salim Al-Muslat, told reporters in Geneva: "We won't accept a postponement to hold illegitimate elections."

The HNC had not been informed by de Mistura of any delay in the next round, but would raise it with him in talks resuming on Monday, he said.

Syrian government negotiators at the talks are coming under unaccustomed pressure to discuss the fate of Assad, whose departure the opposition demands.

De Mistura describes Syria's political transition as "the mother of all issues" and after the latest week of talks, praised the opposition for the depth of their ideas, but criticised the veteran diplomats on the government side for getting bogged down.

Riad Hijab, a former Syrian prime minister who leads the HNC delegation, is due in Geneva on Monday, HNC sources said. – Reuters