The friendly fire incident happened late on Friday as two cars drove past German soldiers without stopping for checks, according to the German army's operations command in Potsdam, Germany.

A German armored vehicle fired upon the two cars, killing the troops inside, when the Afghan troops failed to stop despite repeated warnings.

Regional governor of Kunduz province Momed Omar told reporters that the Afghan soldiers had been on their way to the regional capital, also called Kunduz.

"Unfortunately there were some misunderstandings and the German forces fired on them, killing six army soldiers," he said. "For now I can say that the incident happened mistakenly."

Omar said that action was needed to avoid similar incidents in future. "There should be more coordination in these kinds of operations between the two sides," he said.

A spokesman for the German operations command confirmed five were killed and said the German army regretted the incident, which would be investigated.

However, German Press Agency dpa reporters saw six bodies from the attack at a provincial hospital. NATO and Afghan army officials also confirmed 6 causalities in the shooting.

Local government spokesman Muhboballuh Sayedi said Afghan commanders were meeting on Saturday with coalition forces to discuss what happened.

German chancellor Angela Merkel telephoned Afghan president Hamid Karzai to express her regrets.

Warning as German death toll rises

Meanwhile, the Taliban said it would attack more German troops after three Bundeswehr soldiers were killed in a clash with militants in Kunduz. Eight other German soldiers were seriously injured.

The troops were on a mine-clearing operation when they came under attack by around 100 Taliban fighters, German military officials said.

It was the highest number of casualties the post-war German armed forces have suffered in battle, and it brought the number of German soldiers killed in Afghanistan to 39.

Taliban spokesman Zabiullah Mujahid told the German Press Agency dpa that the militant group had warned the German government and parliament to pull out its troops from Afghanistan, "but they did not listen."

"There will be more casualties inflicted on German force if they continue their presence in Afghanistan," said Mujahid.

The attack happened as German Development Minister Dirk Niebel was in Afghanistan, visiting the German military headquarters in the northern city of Mazaar-i-Sharif. He called the attack "shameful."

Unpopular war

The Bundeswehr's military involvement in Afghanistan is unpopular with the majority of Germans, but Chancellor Angela Merkel and her coalition government see a continuing commitment to the NATO presence in the country as central to German foreign policy.

Germany has around 4,300 troops in the country and is the third-largest NATO contributor to the war. Most of them operate in provincial reconstruction teams, helping to build up Afghanistan's infrastructure, but have increasingly been subject to attacks.

There are currently more than 120,000 NATO-led troops in Afghanistan. Up to 30,000 additional US troops were ordered by US President Barack Obama in December in a bid to turn the tide of eight-year war.

cb/rc/Reuters/dpa/AP
Editor: Andreas Illmer