Top Taliban commanders were gathered inside the madrassa at the time of the attack in the northeastern province of Kunduz, a security source told AFP.

He said an unknown number of civilians were among the casualties that also included senior Taliban commanders who were "planning for the next spring operations".

"Several dead and at least 15 wounded", including children, were taken to the regional hospital in the provincial capital Kunduz, Naim Mangal, a doctor, told AFP.

Relatives of the wounded told an AFP photographer at the hospital that the attack happened during a graduation ceremony for madrassa students.

A defence ministry spokesman confirmed an airstrike in Dashte Archi district but described the location as a kind of Taliban "training centre" and denied civilians were among the casualties.

"Twenty Taliban, including the commander of their Red Unit in the district, and also a key member of the Quetta Shura were killed," Mohammad Radmanish said.

The Red Unit is the insurgent group's elite unit, and the Quetta Shura is the group's leadership council.

The same number were wounded, Radmanish added.

The meeting included a "high-ranking Taliban delegation" from the Quetta Shura, Ghulam Hazrat, a spokesman for the 20th army division in Kunduz, told AFP.

"Fifteen Taliban were killed and 10 were wounded," Hazrat said. He also denied civilians were among the casualties.

A senior local official said "around 150" people had been killed and wounded in the airstrike.

Afghan officials often give conflicting casualty figures after an attack.

Obtaining detailed information is difficult because the Taliban controls the area. Most telecommunication services are cut from late afternoon on Taliban orders, locals say.

A spokesman for US Forces said they were not involved in Monday's airstrike.

Afghanistan's fledgling air force has accelerated bombardments in recent months as the Americans beef up the country's aerial capability with more aircraft and better weapons.

Earlier this month, the Afghan Air Force dropped its first laser-guided bomb on a Taliban compound in the western province of Farah, where the militants have gone on the offensive.

US and Afghan forces are increasing ground and air offensives against Taliban and Islamic State insurgents as they try to get the upper hand in the 16-year war.

The latest airstrike comes weeks before the Taliban usually launches its spring offensive which is expected to be particularly bloody this year.