UNITED NATIONS - The evacuation of civilians from the besieged Syrian city of Homs was a "remarkable" achievement, UN humanitarian chief Valerie Amos said Thursday, though warning 250,000 people across the war-torn country were awaiting help.
Amos said the Homs operation should not serve as a model for future efforts.
"It was a success given the extremely difficult circumstances, but not a progress," she added.
"We evacuated 1,400 people but there (are) nearly 250,000 more to go if you look at all the besieged communities."
Amos told reporters that the UN had received "verbal assurances" from both sides in the conflict that the truce around Homs would be extended but officials were still awaiting written confirmation.
"We can't continue without those written assurances," she said.
Amos called on the 15-member UN Security Council to "use their influence over parties to ensure they abide by pauses, give humanitarian access, commit in writing to upholding international humanitarian laws."
She expressed frustration at the "extremely limited and painstakingly slow" progress.
"That's why we are all not only pessimistic, but so frustrated," she said.
A Western draft resolution under consideration before the Security Council provides for possible sanctions against Syria if humanitarian aid was prevented from reaching its target.
Russia, however, opposes the Western text and has instead drafted a rival resolution.
Moscow's UN Ambassador Vitaly Churkin said the Russian resolution included "some strong language on terrorism," insisting that he believed a compromise could be reached.
"I wouldn't say we are far apart," he said. "What unites us is the realisation that the humanitarian situation in Syria is very grave."
US Ambassador Samantha Power said the West was seeking a resolution "that will make a meaningful difference on the ground."
"For us, given the gravity of the situation, better no resolution than a bad resolution," Power said.