Germany's foreign intelligence chief pledged Wednesday to speed up his agency's response times as part of a revamp over errors in the lead-up to NATO's withdrawal from Afghanistan.

US-led international troops, including Germany, ended a 20-year deployment in the war-ravaged country in a pull-out widely denounced as "chaotic" and a "debacle" for NATO.

The head of the BND foreign intelligence agency, Bruno Kahl, told MPs that a "new organisational framework" would pursue the aim of "faster reaction" to threats abroad.

He acknowledged that the speed of the Taliban takeover in Afghanistan had been "surprising" for the BND foreign intelligence service.

"We must admit that we did not count on the Taliban taking control in Afghanistan and its capital Kabul so quickly," he told an annual parliamentary hearing on Germany's spy agencies.

"We must and want to learn from that."

The German spy chief said the events of August in Afghanistan showed "with what rapid speed the situation on the ground can change".

During the campaign for Germany's September 26 general election, Foreign Minister Heiko Maas pointed the finger at the BND and other secret service agencies for providing what he called "faulty" and incomplete intelligence on the advance of the Taliban.

Kahl said the BND reform would focus on "more closely intermeshing" information collection and evaluation.

In Washington last month, US Defense Secretary Lloyd Austin admitted the Taliban takover and the weakness of the Afghan armed forces "took us all by surprise".

In Wednesday's testimony, the director of Germany's domestic security watchdog spoke of the security risks posed by growing radicalisation at home.

Thomas Haldenwang, head of the Office for the Protection of the Constitution, said right-wing extremism was the "biggest threat to security and democracy in Germany". 

He cited 22,357 criminal offences recorded last year attributed to the far right, including 1,023 acts of violence. 

"We must strengthen our democracy's capability to resist," Heldenwang said.