After a day's delay and repeated bitter recriminations, the warring sides in Syria will hold their first joint meeting on Saturday to launch talks aimed at ending almost three years of conflict.

In a measure of the task ahead, diplomatic sources said the first two days of talks in Geneva would involve discussing a deal to allow aid into a single city, Homs, where people are starving.

The peace conference almost collapsed on Friday, the day face-to-face talks were meant to start, and was only put back on track after United Nations mediator Lakhdar Brahimi persuaded the two sides to focus on smaller issues on which there might be agreement.

"We do expect some bumps on the road," Brahimi told a news conference after separate meetings with the two delegations.

With international divisions over how to end the conflict putting an overall political solution out of reach for now, the two sides will focus on small, confidence-building steps with no certainty negotiations will even last the week.

"Both parties will be here tomorrow...they will not leave on Saturday or Sunday," Brahimi said.

Opposition delegate Anas al-Abdah said the process would begin with a brief meeting at 10 am (0900 GMT) on Saturday at which only Brahimi would speak, to be followed by another longer session in the afternoon.

Even that may not come off.

One diplomatic source, noting the fierce verbal attacks that marked the opening of the conference in the Swiss city of Montreux on Wednesday, said on Friday he had become cautious.

"Compared to 10 days ago, we've had Montreux with both delegations, this start in Geneva with an extra day's delay, tomorrow 30 minutes with the two delegations and then maybe a subject they can agree on. Small steps, but small steps are better than no steps."

"It's clear there will be hysterical episodes each day."

Humanitarian access for Homs, where rebels are surrounded in central districts by forces loyal to President Bashar al-Assad, could be agreed fast.

"The practical aspects have been worked on. Things are ready and if the government doesn't put a block on it then it could happen quickly," a diplomatic source said.

But deep mutual mistrust and the absence from Geneva of powerful Islamist opposition groups and Assad's ally Iran make any substantial progress very difficult.

The opposition said early on Friday it would not meet the government side unless it first agreed to publicly endorse a 2012 statement by world powers calling for a transitional government in Syria.

The government rejected the demand and said its negotiators would leave Geneva unless serious talks began within a day.

After talking to both sides, Brahimi indicated on Friday afternoon their argument, which centres on whether Assad would have to step down, had been put to one side.

"Tomorrow we have agreed that we shall meet in the same room," Brahimi said. The negotiations would be based on the 2012 statement, known as Geneva 1, which he acknowledged was subject to differing interpretations.

"We wanted these delegations nominated months ago to prepare things better," he said.

Diplomats are playing down any hopes of progress.

"Expectations are so low we'll see how things develop day by day," a Western diplomat said.

Brahimi had already indicated that his aim was to start by seeking practical steps, such as local ceasefires, prisoner releases and access for international aid deliveries, before embarking on the tougher political negotiations.

"I think an immediate political solution is unrealistic, unfortunately," French Foreign Minister Laurent Fabius told France 24 television.

Syria's civil war has already killed at least 130,000 people, driven more than a third of the country's 22 million people from their homes and made half dependent on aid, including hundreds of thousands cut off by fighting.

Among the hurdles to progress, the Islamist militants who control most rebel-held territory are boycotting the talks and say anyone attending negotiations that fail to bring down Assad would be traitors.

Assad's main regional backer, Iran, is also not represented at the Geneva talks. UN Secretary-General Ban Ki-moon invited Tehran at the last minute, but then withdrew the invitation 24 hours later when it refused to endorse the Geneva 1 protocol.-Reuters