GENEVA — Airstrikes by the American-led coalition against Islamic State targets have killed hundreds of civilians around Raqqa, the militant group’s last Syrian stronghold, and left 160,000 people displaced, a United Nations panel said on Wednesday.

The findings of the panel, which has been documenting the war in Syria with periodic reports almost since the conflict began more than six years ago, reinforced fears by humanitarian groups over the heavy loss of civilian life that would result from the American-led coalition’s airstrikes.

Paulo Sérgio Pinheiro, the Brazilian diplomat who leads the panel, said the airstrikes had escalated as an American-backed militia known as the Syrian Democratic Forces moved recently to retake Raqqa, which Islamic State fighters seized in 2014 and made their de facto capital.

“We note in particular that the intensification of airstrikes, which have paved the ground for an S.D.F. advance in Raqqa, has resulted not only in staggering loss of civilian life, but has also led to 160,000 civilians fleeing their homes,” Mr. Pinheiro said in a report, presented to the United Nations Human Rights Council in Geneva.