In a statement released on Monday, the mission said the "aerial operations" were conducted "against reported drug manufacturing facilities" and that it was "actively looking into" those allegations, presstv reported.
"The locations are not easily accessible and there are numerous operational challenges to the verification" of civilians being harmed, UNAMA added.
Afghan Interior Ministry Spokesman Nasrat Rahimi stated that "150 Taliban terrorists were killed, 40 wounded" in the Farah operations. However, the Taliban denied the facilities were used for drugs and claimed "up to 100" civilians had been killed.
Last month, the mission published a report saying civilians are for the first time being killed in greater numbers by US and pro-government forces than by the Taliban and other militant groups.
"There can be absolutely no justification for deliberate or indiscriminate attacks against civilians," Tadamichi Yamamoto, UN Secretary-General's Special Representative for Afghanistan, said in the UNAMA statement, adding, "It is particularly egregious that a premeditated act of extreme violence was conducted against a development agency where civilians were striving to improve the lives of all citizens."
The United States has recently stepped up its air raids in an attempt to exert pressure on the Taliban to accept a negotiated end to its 18-year insurgency.
The UN mission in Afghanistan recorded 649 civilian casualties as a result of aerial attacks in the first nine months of last year, the highest number in any year since systematic recording began in 2009.