BEIRUT, Lebanon  More than 80 people, including a large number of civilian refugees, were killed in a government airstrike in northern Yemen on Wednesday as they sought shelter from a monthlong conflict between the military and rebel forces, provincial tribal leaders said.

Local and international human rights groups have condemned the attack, which appeared to be the deadliest single episode in a worsening war between government forces and the Houthi rebels in Yemen’s remote and mountainous north.

The airstrike took place in Adi, outside the rebel-controlled town of Harf Sufyan, where refugees from the conflict had gathered under trees and plastic tents, according to tribal figures in the area who asked not to be identified out of fear for their safety. Dozens of people were also wounded in the attack, they said.

It was not immediately possible to confirm the number of casualties, but several aid groups and Yemeni news sources reported a death toll higher than 80.