Smoke rises after a recent airstrike during fighting between members of the Syrian Democratic Forces and Islamic State militants in Raqqa, Syria. (Zohra Bensemra/Reuters)

The United Nations urged international powers to ease military operations around the Islamic State’s de facto capital Thursday amid intensifying concern about the safety of thousands of civilians trapped inside the northern Syrian city.

The rare call to pause hostilities in Raqqa underscored the severity of the humanitarian crisis there. As Islamic State militants use snipers and threats of arrest to prevent residents from fleeing, monitoring groups have blamed U.S.-led coalition forces for hundreds of civilian deaths.

“On Raqqa, our urging today from the U.N. 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 U.N. special envoy on Syria, told reporters in Geneva.

[U.S.-led airstrikes are killing hundreds of civilians in the battle for Raqqa, groups say]

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.

As the Islamic State’s most important stronghold, Raqqa became a symbol of the militant group’s ambitions to hold and govern vast swaths of territory. But the infrastructure in the city has crumbled as the Islamic State has come under heavy bombardment, and its income has dried up as it loses territory elsewhere.

Aid groups estimate that more than 16,000 people remain in 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 Washington, a State Department spokesman said any pause in operations could give the Islamic State “more time to build up its defenses and thus put more civilians in harm’s way” and “reinforce [its] tactics of using civilians as human shields, putting even more civilians at risk. There are no simple solutions in such a complex situation.”

[A photographer’s journey into the dying center of the Islamic State]

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

Displaced Raqqa residents told researchers from the human rights group visiting the surrounding province that they had faced Islamic State booby traps and snipers as they fled, as well as artillery attacks and airstrikes by the coalition and its allied, Kurdish-led ground force, also known as the Syrian Democratic Forces (SDF). “Thousands of civilians are trapped in a deadly labyrinth where they are under fire from all sides,” said Donatella Rovera, Amnesty’s senior crisis response adviser. “Knowing that IS use civilians as human shields, SDF and U.S. forces must redouble efforts to protect civilians.”

Amnesty also documented allegations that Syrian government forces had dropped unguided munitions and cluster bombs close to villages and displacement camps south of the Euphrates River.

Carol Morello in Washington contributed to this report.

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