Amid intensifying concern about the safety of thousands of civilians trapped inside the northern Syrian city of Raqqa, the United Nations has called on international powers to ease military operation around Islamic State’s de facto capital.

As Islamic State militants use snipers and threats of arrest to prevent residents from fleeing, monitoring groups have blamed US-led coalition forces for hundreds of civilian deaths.

According to The Washington Post, the rare call to pause hostilities in Raqqa underscores the severity of the humanitarian crisis there.

“On Raqqa, our urging today from the UN side to the members of the humanitarian task force… is that they need to do whatever is possible to make it possible for people to escape Raqqa,” Jan Egeland, senior humanitarian adviser to the United Nations’ special envoy on Syria, told reporters in Geneva.

More than 270,000 people have fled the city since the coalition offensive began, and many of them are stuck in ramshackle camps in the Syrian desert.

Aid groups estimate that more than 16,000 people remain inside the half of the city still controlled by Islamic State forces, many surviving on paltry supplies of food and little to no electricity.

“Now is the time to think of possibilities, pauses or otherwise, that might facilitate the escape of civilians, knowing that Islamic State fighters are doing their absolute best to use them as human shields,” Egeland said.

In a report released by Amnesty International, the city is described as a “deadly labyrinth.”