WASHINGTON (AFP) - The United States said Thursday that the Syrian opposition has made "legitimate" demands for aid to besieged areas but nevertheless urged it to attend planned peace talks in Geneva, Switzerland, on Friday. The main Syrian opposition coalition announced it would not attend the UN-brokered talks until a deal is struck to supply food and care to beleaguered civilians. Washington, while expressing sympathy for the rebel demands, said it was important to maintain momentum in the peace process.

"This is really an historic opportunity for them to go to Geneva to propose serious, practical ways to implement a ceasefire and other confidence-building measures," State Department spokesman Mark Toner said. "We still believe they should do so without preconditions. We believe these demands, while legitimate, shouldn't keep the talks from moving forward."

The spokesman cited UN estimates that 486,000 Syrians are trapped in besieged areas, with 274,000 of them surrounded by forces loyal to Bashar al-Assad's regime.

"All parties must allow for immediate, unconditional and unfettered humanitarian assistance to reach those in need in all of the besieged areas," Mr Toner said.

He insisted that the opposition's anger on this point should not be a reason to delay or abandon the talks, which Washington sees as key to kick-starting a peace process.

The UN says that more than a quarter-million Syrians have died in the war, soon to enter its fifth year. Millions of others have fled the country.