Pakistan's forces struck Kabul and the eastern border province of Nangarhar on Monday, claiming to have hit military installations and "terrorist support infrastructure".

But the Taliban authorities in the Afghan capital on Tuesday said that around 400 people were killed at a drug rehabilitation centre in the capital, with more than 200 wounded.

NRC country director Jacopo Caridi said the NGO had teams on the ground in the immediate aftermath of the strikes to assist in the rescue effort.

"From what we saw and what we discussed with the others involved in the (emergency) response, we can say that there were hundreds of killed and wounded," he told AFP.

Immediate independent confirmation of exact tolls is difficult in Afghanistan, with attacks often in hard-to-reach places and contradictory information from officials.

Pakistan, which accuses Afghanistan of harbouring militants who have attacked its territory, has said Taliban government claims that the clinic was targeted are "entirely baseless".

Caridi confirmed that the medical facility in Kabul was hit and that one of its buildings was "completely burned and destroyed".

Rescue teams were still trying to remove bodies from the rubble on Tuesday morning and to find ways of accessing parts of the compound where walls had collapsed, he added.

He described the scene, which included body parts in the debris, as "shocking" and indicated that identification of the victims and settling on a definitive toll was not clear.

"In Europe, we have the systems to identify the people, even from body parts," he added.

"But here, I don't know if they have these systems. But what I saw was a finger in one place, a foot in another place, a hand in one location. It was really horrific," said Caridi.