Syria's main opposition High Negotiations Committee (HNC) told AFP Friday it was willing to join a transitional government with diplomats and technocrats from President Bashar al-Assad's government.

But the HNC maintained that Assad's departure from office must be part of any peace deal and categorically ruled out working with anyone who played a central role in the civil war which has killed more than 270,000 people and displaced millions.

"We cannot accept the participation of the parties who committed crimes against the Syrian people in the transitional governing body," HNC spokesman Salem al-Meslet said on the sidelines of peace talks in Geneva.

The opposition, however, could cooperate with regime "diplomats and technocrats", provided they had support among the population.

He also said it was "premature" to discuss specific individuals who could be included in a prospective new government.

"The distribution of seats of the transitional governing body will be subject to a long debate," al-Meslet told AFP.

A new round of UN-brokered Syria peace talks got underway earlier this week.

The government delegation arrived in Geneva on Friday and held its first meeting with United Nations mediator Staffan de Mistura.

Lead government negotiator Bashar al-Jafaari described the meeting as "constructive and fruitful".

Political transition in the war-ravaged country, and particularly Assad's future, are the key obstacles at the negotiations, which aim to set up an interim government in six months ahead of UN-monitored presidential and parliamentary elections within 18 months.

At the last round of talks, the HNC put forward a detailed plan on political transition, but the regime remained focused on general principles and made clear it was not yet ready to tackle the concrete details of a new government.

De Mistura has urged Damascus to take a step forward at this round by laying out on paper its vision for a unity government.

The HNC was holding its second meeting with de Mistura on Friday evening, with the government due to meet the UN again on Monday.

This round is expected to last 10 days.

The UN hopes that both sides will leave Geneva with general agreement on how to progress towards a new government.

Before the talks began, de Mistura travelled to Moscow and Tehran to meet with key Assad allies to shore up support for his peace drive.

He has repeatedly said outside influence, especially from Moscow, was crucial to success at the intra-Syrian talks.

The negotiations, during which opposing sides meet separately with the UN, have been overshadowed by intensifying violence on the ground that has further threatened a fragile ceasefire declared on February 27.

Fierce fighting raged Friday around Syria's Aleppo as government forces have battled jihadists from the Islamic State group and Al-Qaeda linked Al-Nusra, who are not part of the ceasefire.

The surge in violence forced tens of thousands more to flee their homes.