GENEVA: Syria's government and opposition sat down Tuesday for their first face-to-face talks this month, on the second day of a new round of rocky peace negotiations.

The talks in Geneva were being chaired by UN-Arab League mediator Lakhdar Brahimi, the United Nations said.

"The Joint Special Representative is meeting this morning with the two delegations simultaneously. The meeting started at 10:00 am (0900 GMT)," UN spokeswoman Corinne Momal-Vanian said in an email to reporters.

The second round of the so-called Geneva II talks got off to a shaky start Monday, with Brahimi shuttling between the delegations in the hope that keeping them apart at first might put them in a more conciliatory state of mind.

An eight-day session last month achieved little beyond getting the foes into the same room for the first time since Syria's civil war erupted in March 2011.

There has been little sign that the current round, expected to last until Friday, will make progress towards ending the conflict.

More than 136,000 people have died and millions have been forced from their homes since the war broke out after the regime of President Bashar al-Assad cracked down on Arab Spring-inspired protests.

The two sides spent Monday trading blame for escalating violence and for difficulties evacuating civilians and getting aid to opposition-held districts of the city of Homs, under government siege since 2012.

And neither appeared prepared to budge an inch on their negotiating positions.

The opposition says the only way to end the war is to form a transitional government -- without Assad.

The regime insists his future is not up for negotiation and insists the talks must focus on halting "terrorism" -- its term for a revolt which it says is fuelled by foreign jihadists and Gulf money.

The opposition warned Brahimi that it will not return for more talks if there is no progress this week.

"We're not going to run away" if there is a glimmer of hope, but if there is no progress "let us not pretend we are doing something," spokesman Louay Safi said Monday.

He said that in such a case it would be "more honest to say we have failed", although he acknowledged the only alternative was to continue fighting.

The opposition delegation this time includes seven representatives of fighters on the ground, though they do not have a seat at the negotiating table, Safi said.

With the talks at an apparent standstill, Russia on Monday proposed that Moscow and Washington hold a collective meeting with the UN and the two sides to break the deadlock.

The United States, which backs the opposition, and Russia, a key ally of Syria, initiated the so-called Geneva II talks and pushed for eight months to get the parties to the table.

Safi said while the opposition was "very disappointed" over Russia's continued backing of Assad, it would support the joint talks.

"If this is what it will take to make the regime negotiate a political solution, then we welcome that," he said.