The strike was carried out last Wednesday on a training camp in the eastern province of Khost near the border with Pakistan, local authorities said.
They said it was launched by the United States. There was no immediate confirmation from the US-dominated NATO force which is combating Taliban and other militants in Afghanistan.
It is unclear how many people were killed. The Khost provincial governor Hukum Khan Habibi put the figure as high as 50 but that could not be confirmed.
"I myself attended the funeral prayer for four fighters, villagers told me they were mujahideen," said Alamzeb Khan, a district official in Lower Dir.
Also Read
Khan said the coffins were wrapped in the flag of Al Badr, a Pakistani militant group linked to the Taliban, and guests at the funeral shouted jihadi slogans against US troops in Afghanistan.
The bodies were badly mutilated, and one villager who attended the funeral said the names of the fighters had been written on the wooden coffins for identification.
Governor Hukum Khan Habibi said the strike was staged on Wednesday. "In this incident, more than 50 Pakistani fighters were killed."
Faizullah Ghairat, Khost provincial police chief, confirmed the attack and said it was carried out by the US.
In June 2014 the Pakistani army launched a major attack on militants operating in Pakistan's tribal areas on the border, where they had previously been operating with impunity, driving many into Afghanistan.
US drone strikes have long targeted militants hiding along the porous border between the two countries.