US airstrikes in Afghanistan’s Helmand province may have been responsible for the deaths of at least 18 civilians, mostly women and children, according to the UN and local sources.

Airstrikes took place late on Thursday in Sangin district, which has been highly contested for most of the Afghan war.

It is the first claim of civilian casualties at the hands of US forces in Afghanistan since Donald Trump assumed the US presidency, and comes two weeks after a botched US raid in Yemen allegedly killed dozens of civilians.

The UN said on Sunday: “On 9 and 10 February, international military forces conducted airstrikes in Helmand’s Sangin district reportedly targeting anti-government elements. [The UN’s] initial enquiries suggest that the airstrikes killed at least 18 civilians, nearly all women and children.”

Brig Gen Charles H Cleveland, a spokesman for the international coalition, confirmed that the US conducted approximately 30 airstrikes in Sangin last week.

“We are investigating the allegations and working diligently to determine whether civilians were killed or injured as a result of US airstrikes conducted in support and defence of Afghan forces in or around Sangin,” he said.

The Afghan defence ministry declined to comment, but a government spokesman, Najeeb Danesh, said a delegation from the ministry was investigating.

Haji Ahmand, who lives in Sangin, was in Kandahar when a bomb hit his brother’s house at about 2am. Waiting to visit his wounded relatives outside a hospital in Lashkar Gah, Helmand’s capital, he said two boys and two women from his family were killed. The bodies were dug out from under the rubble by Afghan national army soldiers and brought to the hospital, Ahmand said.

“What the Americans are doing in Helmand is not right. They target the locals instead of [the] Taliban. The Taliban are far from my brother’s house,” Ahmand said. “We would prefer if the Americans would just leave us alone.”

In 2016, the UN documented the highest number of civilian casualties of the 15-year Afghan war. According to a report, the number of civilians killed and injured in airstrikes was double that of the previous year, with foreign forces responsible for half. Nearly 1,000 children were killed in the Afghan conflict last year, a yearly rise of 24%.

In another attack in Helmand on Saturday, a car bomb targeting an Afghan army Humvee killed seven civilians, according to the UN, and injured at least seven more. Most of the injured were child street vendors.

Additional reporting by Abdurrauf Mehrpoor in Lashkar Gah