NATO defence ministers made no decision on whether or when to pull out of Afghanistan at a meeting on Thursday, Secretary-General Jens Stoltenberg said, adding that the allies faced a dilemma as violence increases again.

After two decades of Western military intervention and hundreds of billions of dollars in investment, NATO countries are reluctant to heed a May 1 deadline and risk undermining progress towards democracy as a peace process stalls.

"At this stage, we have made no final decision on the future of our presence," Stoltenberg said after a video conference with allied defence ministers. "As the May 1 deadline is approaching, NATO allies will continue to closely consult and coordinate in the coming weeks," he told a news conference.

German Defence Minister Annegret Kramp-Karrenbauer said on Wednesday that the Taliban must do more to meet the terms of a 2020 agreement with Washington on the withdrawal of US forces to allow a pullout of the foreign troops.

The Biden administration, in office since Jan. 20, is conducting a review that will determine the status of the 2,500 American troops remaining in Afghanistan, where they now are outnumbered by allied soldiers.

US Secretary of State Antony Blinken discussed the review in a telephone call on Wednesday with Afghan President Ashraf Ghani, reiterating US support for the peace process, the State Department said.

Attacks in Afghanistan, including a bomb that killed the deputy governor of the capital Kabul in December, have prompted members of the US Congress and international rights groups to call for a delay to the pullout, agreed when Donald Trump was US president.

"We are faced with many dilemmas, and there are no easy options," Stoltenberg said.

"If we stay beyond the first of May, we risk more violence, more attacks against our own troops ... But if we leave, then we will also risk that the gains that we have made are lost."

US Defense Secretary Lloyd Austin promised to consult with allies and partners on the way forward, Stoltenberg added.