The International Criminal Court's new prosecutor sought Monday to relaunch an investigation into Afghanistan, focusing on the Taliban and the Islamic State-Khorasan group while alleged US crimes will take a back seat.

Karim Khan, who took over in June, said the situation in Afghanistan following the Taliban's takeover last month meant war crimes were no longer likely to be investigated properly.

A lawyer for alleged victims of US torture in Afghanistan said she was "stunned" after Khan announced he would "deprioritise" the investigation into American forces, a probe that has long enraged Washington.

The Hague-based ICC's inquiry had been put on hold in 2020 after the now-deposed government in Kabul said it would try to investigate war crimes allegations itself.

Set up in 2002 to tackle the world's worst crimes, the court has the authority to step in where national governments are unable or unwilling to bring people to justice for war crimes.

But Khan said that the "current de facto control of the territory of Afghanistan by the Taliban, and its implications (including for law enforcement and judicial activity in Afghanistan) represents a fundamental change in circumstances necessitating the present application."

The ICC's limited resources and the need to focus on cases most likely to result in convictions meant he would now narrow his focus in Afghanistan, Khan added.

"I have therefore decided to focus my office's investigations in Afghanistan on crimes allegedly committed by the Taliban and the Islamic State-Khorasan Province ("IS-K") and to deprioritise other aspects of this investigation," he said.

This was because of the "gravity, scale and continuing nature of alleged crimes by the Taliban and the Islamic State", Khan said.

The ICC prosecutor specifically mentioned the deadly August 26 attack on Kabul airport claimed by IS-K in which 13 US service members and more than 100 Afghan civilians were killed
The ICC prosecutor specifically mentioned the deadly August 26 attack on Kabul airport claimed by IS-K in which 13 US service members and more than 100 Afghan civilians were killed AFP / Wakil KOHSAR

The prosecutor added that the Taliban's takeover "may constitute an unconstitutional transition of power" and added that "there is a reasonable basis to believe that persons affiliated with the Taliban committed crimes against humanity."

Reports of the Taliban's release of "thousands of prisoners allegedly linked to Al-Qaeda and IS terror groups... does not support the notion that the Taliban will genuinely investigate".

The ICC prosecutor also specifically mentioned the deadly August 26 attack on Kabul airport claimed by IS-K in which 13 US service members and more than 100 Afghan civilians were killed.

The Afghan investigation has been one of the ICC's most controversial.

Khan's predecessor Fatou Bensouda was hit with sanctions by the US administration of president Donald Trump over the Afghanistan probe and an investigation into the Palestinian territories.

Current President Joe Biden has lifted the sanctions.

Khan indicated that the ICC would keep its eye on possible US crimes.

"In relation to those aspects of the investigation that have not been prioritised, my office will remain alive to its evidence preservation responsibilities, to the extent they arise," he said.

But the decision to end the ICC focus on US abuses in Afghanistan was greeted with fury in some quarters.

"Stunned," tweeted Katherine Gallagher, a lawyer for Afghan victims of what they say was torture by US forces, adding that Khan had given them no advance warning of the move and they only found out when they read a press release.

"Next time I'm told about "victim-centered" #ICC by court officials or diplomats, academics... #SHAME", added Gallagher.