Syrian rebels
Syrian rebelsReuters

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, AFP reported.

The call came hours after the main Syrian opposition coalition announced it would not attend UN-brokered talks in Geneva until a deal is struck to supply food and care to beleaguered civilians.

Talks had been due to start on Friday, and 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, according to AFP.

"And we still believe they should do so without preconditions," he said, adding, "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, 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," Toner said.

But 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.

United Nations envoy Staffan de Mistura has invited the Saudi-backed High Negotiations Committee (HNC), a rebel umbrella group, to send delegates to indirect talks in Geneva.

But the group, which is meeting in Riyadh, said earlier this week it was waiting for "clarifications" on the guest list for the planned dialogue.

The Committee has insisted it must be the sole opposition delegation, while the United Nations has issued invitations to other groups it sees as regime opponents.

The talks have already been delayed from their scheduled start this past Monday over who will represent the opposition.

Assad's regime has designated its UN envoy Bashar al-Jaafari as its chief negotiator.