Afghan girls carry their belongings on Thursday, Oct. 6, 2016, outside the Samarkhel Encashment Center near Jalalabad in eastern Afghanistan, where thousands of Afghan refugees returning from Pakistan are registered and given cash and other assistance.

KABUL, Afghanistan — The United Nations has expressed grave concern over escalating violence in Afghanistan’s southern Helmand province, where it says airstrikes by international forces likely killed more than a dozen civilians, mostly women and children.

U.S. Forces-Afghanistan said initial findings of an investigation it is conducting showed no evidence that civilians were killed in the strikes on Thursday and Friday in the hotly contested district of Sangin.

Afghan and coalition forces have been relying increasingly on air power in an effort to stem further advances by the Taliban, who are now said to control 10 percent of the country’s districts and contest 33 percent of them.

“Initial enquiries suggest that the airstrikes killed at least 18 civilians, nearly all women and children,” the U.N. said in a statement late Sunday, referring to its own investigation.

U.S. troops have been helping Afghan forces battle the Taliban in and around Sanqin, where the militants are reported to have based themselves in residents’ homes. Two American soldiers were injured in the fighting on Thursday.

Initial reports said the international airstrikes killed as many as 25 civilians.

USFOR-A officials said they had conducted about 30 strikes in Sangin over the past several days.

The Helmand governor’s office said Monday that its initial assessment on Saturday that no civilians were killed was incorrect.

“Now our investigation shows that five civilians, including four women and a man were killed in the operation,” said Omar Zwak, spokesman for Helmand’s governor. He said that number could rise as their investigation continues.

Airstrikes by Afghan and international forces caused 590 civilian casualties, including 250 deaths, last year — nearly double the number recorded in 2015 and the highest since 2009, the U.N. said in a report released last week.

Zubair Babakarkhail contributed to this report.

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