An airstrike designed to target Islamic State militants in Nangarhar, eastern Afghanistan, has killed at least 15 civilians and injured another 13, including a child. The UN said the strike was carried out by an international drone, which only the US operates.

The United Nations Assistance Mission in Afghanistan (UNAMA) has condemned the killing of the civilians, calling on the Afghan government and international military forces to launch a “prompt, independent, impartial, transparent, and effective investigation into the incident.” The airstrike took place in the Achin district of the Nangarhar province, on the eastern border with Pakistan, early Wednesday morning.

The UN said the civilians had gathered in a village to celebrate the return of a tribal elder from the Hajj pilgrimage to Mecca and were sleeping in a guesthouse of the elder when the airstrike took place.

“A drone targeted the house and killed most of them,” Mohammed Ali, the Achin district police chief, told Reuters.

Civilian victims of the strike included students and a teacher, according to the UN.

“I saw dead and wounded bodies everywhere,” Raghon Shinwari, who was injured in the attack, told Reuters, speaking from a hospital bed in Jalalabad city.

Afghan government sources told the UN mission that Islamic State (IS, formerly ISIS/ISIL) personnel also died in the attack. Provincial police spokesman Hazrat Hussain Mashriqiwal confirmed that several IS leaders had been killed, but denied there were any noncombatants among the victims, Reuters reported.

The US military acknowledged it had conducted an aerial attack in Nangarhar, but refused to discuss the incident.

“We won’t discuss the details of the specific counter-terrorism operation conducted in Nangarhar on 28 September because we are still reviewing all materials related to the strike,” it said in a statement on Wednesday.

“We take every possible measure to avoid civilian casualties in these operations, and will continue to work with Afghan authorities to determine if there is cause for additional investigation as we partner with the Afghan government in the broader fight against terrorism.

“We will continue our mission to degrade, disrupt, and destroy Daesh [Arabic pejorative for IS] and to help our Afghan partners to do the same.”

The US military told the AP that it had been conducting air operations against IS loyalists in Achin at the time. The spokesman for US forces in Afghanistan, Brig. Gen. Charles Cleveland, said in a statement that US forces were working “with Afghan authorities to determine if there is cause for additional investigation.”

The US mission in Afghanistan has dragged out much longer than originally anticipated, with President Barack Obama canceling the initial plan to withdraw the majority of troops in 2014 in exchange for a blueprint to scale back forces by early 2017. In July this year, Washington announced that the US will leave 8,400 troops through the end of the Obama administration, citing an increase in Taliban attacks.

The Taliban has been around in Afghanistan for the last two decades, while Islamic State activities were reported in Afghanistan in late 2014. Though the Al-Qaeda offshoot treats other extremist groups in the region with skepticism, it has opted for a “non-aggression pact” with IS.

The US bears full responsibility for the deteriorating situation in Afghanistan, Zamir Kabulov, who served as Russian envoy to Afghanistan in 2004-2009, said earlier this month.

Washington “cut back their presence [in Afghanistan] and did not resolve a single issue and created more problems. They carry political and moral responsibility for what is taking place in Afghanistan now,” he noted.