Neither of the warring sides in the Syria peace talks under way in Geneva was prepared to give up despite two days of deadlock, the UN mediator in the negotiations said.

Lakhdar Brahimi vowed to push ahead with the talks and said he remained hopeful that an agreement to help people in besieged areas of Homs would translate into action on the ground.

"Nobody is walking out, nobody is running away," Mr Brahimi told reporters after cutting short a fourth day of talks aimed at ending the bloody civil war that has claimed 130,000 lives.

The UN-Arab League envoy stressed that neither party bore the blame for his decision to cancel the afternoon session after morning talks remained stuck.

"We have not achieved any breakthrough, but we are still at it, and this is good enough as far as I'm concerned," Mr Brahimi said, adding that he was hoping for "a better session tomorrow morning".

His comments followed a flurry of statements from both sides blaming the other for obstructing the morning's talks.

The talks were marked by the regime delegation's harsh condemnation of a report that the US Congress had secretly approved funding for weapons deliveries to "moderate" Syrian rebel factions.

Mr Brahimi rejected the regime's contention that the US, which along with Russia instigated the peace talks, was not dedicated to their success.

"I believe that they are serious and they want this track to be successful ... There is no doubt concerning that," he said.

In the only bright spot at the talks so far, Mr Brahimi said on Sunday the regime had agreed to allow women and children safe passage from besieged rebel-held areas of Homs.

But there has been no movement since, on either an evacuation or opposition demands that aid convoys instead be allowed in.

"The convoy is ready and still waiting to enter. The authorisation has not been given yet," Mr Brahimi said. "We haven't given up on that." 

Elsewhere, UN Secretary-General Ban Ki-moon has suggested in a report that an operation to remove Syria's chemical weapons had been unnecessarily delayed.

He urged the government of Syrian President Bashar al-Assad to speed up the process.

Under a deal negotiated by Russia and the US, Syria agreed to destroy its chemical weapons arsenal after a sarin gas attack on 21 August, which killed hundreds of people and led to threats of US air strikes.

The Syrian government and rebels blamed each other for the attack.