Delil Souleiman, AFP | Smoke billows in Raqqa's western al-Darya neighbourhood on August 14, 2017, as Kurdish-led forces battle to retake the city from the Islamic State (IS) group.

The United Nations called Thursday for a humanitarian pause to allow an estimated 20,000 trapped civilians to escape the Syrian city of Raqqa, and urged the US-led coalition to rein in air strikes that have caused casualties.

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The Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab fighters backed by US-led coalition warplanes, entered the city in June and have captured nearly 60 percent of it from the Islamic State (IS) group.

But the fighting has proved increasingly bloody for civilians still trapped in Raqqa, with one monitor reporting 167 civilians have been killed in coalition strikes in and around the city since August 14.

"Boats on the Euphrates must not be attacked, people who come out cannot risk air raids when they come out," Jan Egeland, the UN's humanitarian adviser on Syria, told reporters in Geneva.

"So 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 keep them in place," he said.

Earlier on Thursday, Amnesty International warned that civilians fleeing the battle faced a “deadly labyrinth”, coming under fire from all sides.

"Knowing that IS uses civilians as human shields, SDF and US forces must redouble efforts to protect civilians, notably by avoiding disproportionate or indiscriminate strikes and creating safe exit routes," said Donatella Rovera, Amnesty International's Senior Crisis Response Advisor.

The US-led coalition says it takes all possible precautions to avoid civilian casualties.

"We are the good guys and the innocent people on the battlefield know the difference," US Defence Secretary Jim Mattis said on Tuesday.

But the coalition acknowledges it has escalated its strikes on Raqqa, with more aircraft available since a US-backed operation successfully pushed the IS group from Mosul in neighbouring Iraq last month.

The coalition earlier this month acknowledged the deaths of 624 civilians in its strikes in Syria and Iraq since 2014.

But rights groups say the actual figure is much higher, and Amnesty has criticised the coalition's investigation methods for failing to include site visits or witness interviews.

(FRANCE 24 with AFP, REUTERS)

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