ISLAMABAD - The United Nations said Wednesday recent U.S. airstrikes on alleged drug-processing facilities in Afghanistan that killed more than 30 civilians, including children, were "not lawful."

The casualties occurred last May in western Farah and adjoining Nimroz provinces where the U.S. bombed more than 60 sites, identifying them as drug-production plants, according to "extensive fact-finding" into the incident by the U.N. Assistance Mission in Afghanistan (UNAMA). The report said investigators have confirmed 30 deaths and at least four injuries in Farah.

"UNAMA has received reliable and credible information to substantiate at least a further 37 additional civilian casualties [30 deaths and seven injured], the majority of whom were women and children. It is working to further verify these civilian casualties," the report said.

The U.S. military swiftly disputed the charges, questioning the methods and credibility of the sources used by UNAMA.

"The precision strikes against Taliban methamphetamine labs and Taliban combatants in the early hours of May 5, 2019 accurately targeted and struck sources of Taliban revenues used to fund ongoing indiscriminate violence against innocent Afghans," the military noted in a written statement.

In addition to imagery collection during the precision strikes, the U.S. military conducted "exhaustive assessments" of the facilities and surrounding areas after the strikes, it explained.

But UNAMA insisted in its report that the victims inside the facilities were non-combatants because they were not involved in hostile activities and were entitled to protection against such attacks.

"However, according to international humanitarian law, including international customary law, facilities that contribute economically or financially to the war effort of a party to a conflict are considered civilian objectives," UNAMA insisted in its report.

U.S. forces also have targeted drug-production facilities in Afghanistan to try disrupt what is believed to be a major source of revenues for the Taliban.

UNAMA emphasized in its report, however, this was the first time it has received reports of a large number of civilian casualties resulting from such an operation.

American forces launched counter-narcotics airstrikes between 2017 and 2018 in opium-poppy producing southern Afghan provinces where the Taliban controls large swaths of territory. Critics say however the campaign has had little impact and ave drawn strong criticism from Afghan farmers who mostly rely on earnings from poppy cultivation to support their families.