BARREL BOMBS
While the two sides met in Geneva, clashes continued across Syria. The Syrian Observatory for Human Rights reported fighting between rebels and Assad's forces in south Damascus and a series of army air raids across the country, particularly in northern Aleppo and the suburbs outside of Damascus.
Helicopters launched three series of barrel bomb attacks on the suburb of Daraya, the Britain-based monitoring group said, and internecine rebel clashes also continued in the provinces of Hassakeh and Aleppo.
Brahimi said plans for aid to central Homs, where insurgents are surrounded by Assad's forces, were discussed by UN officials and the city governor and supplies could be delivered within 24 hours of a green light from Damascus.
But a Western diplomat said Bashar Jaafari, Syria's UN ambassador who led the government delegation on Saturday, expressed surprise at the proposal even though the diplomat said it had been floated more than a week ago by the United States, Russia, the United Nations and Red Cross.
"The regime's response was: 'This is all new to us'," the diplomat said. "I'm pretty sure it's a stalling tactic."
Opposition spokesman Louay Safi described Homs as a barometer of the government's good intentions. "If the regime doesn't want to bring aid into an area where people are starving then we have a problem," he said. "They are building wells and eating grass and leaves to survive."
Sunday's talks are expected to deal with opposition demands for the release of women and children from Syrian jails, before the talks move on to address on Monday the hotly disputed issue of the transitional governing body.
Profound mutual mistrust and the absence from Geneva of powerful Islamist opposition groups as well as Assad's ally Iran make any substantial progress very difficult, and previous aid deals and ceasefires in Syria have proved short-lived.
The crisis flared with street protests against Assad's rule in March 2011 and descended into an armed insurgency and civil war after security forces put down demonstrations with force.
There are now hundreds of rebel groups across the country, including hardline Islamists and al Qaeda-linked militants. Few pay heed to the opposition in exile and the powerful Islamic Front has said negotiators who return from Geneva without having assured Assad's downfall will be treated as traitors.
Diplomats say Brahimi is trying to secure progress over the weekend on humanitarian aid, local ceasefires and prisoner releases to build up support inside Syria for the talks, before embarking on the tougher political negotiations.
"Brahimi has been very clear - he will spend two days on confidence-building measures. The opposition agreed, but said two days only," the diplomat said.
Syria's civil war has made half of the 22 million population dependent on aid, including hundreds of thousands cut off by fighting.