The Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab fighters backed by US-led coalition warplanes, has retaken 60 percent of Raqqa from the jihadists, but up to 25,000 civilians remain trapped in IS areas, according to UN estimates.
"Now is the time to think of possibilities, pauses or otherwise that might facilitate the escape of civilians," Jan Egeland, head of the UN's humanitarian taskforce for Syria, told reporters in Geneva.
People in Raqqa face a "deadly labyrinth", coming under fire from all sides, Amnesty International said, as the death toll from coalition airstrikes and SDF shelling continued to mount.
Egeland said any humanitarian pause would of course not involve IS, which is doing its "absolute best to use (civilians) as human shields."
"Our urging today from the UN side to the members of the humanitarian taskforce is that they need to do whatever is possible to make it possible for people to escape Raqqa," Egeland said.
The taskforce includes several nations supporting the SDF, including the United States.
This satellite image shows a bakery in Raqqa, Syria on June 2, 2017, left, and on July 19, 2017, right. Source: CNES 2017, Distribution AIRBUS DS
"People that come out cannot risk (being killed by) air raids," Egeland added.
The UN has previously pushed for such pauses on humanitarian grounds, with mixed results, at other points in the Syrian conflict, notably in the battle for Aleppo, when besieged civilians faced severe food and water shortages.
But in the Aleppo fighting between rebels and government forces the UN was able to negotiate with multiple sides, a circumstance that does not apply in IS-held Raqqa.
"I cannot think of a worse place on earth now," said Egeland.
