German troops are based in a relatively quiet part of Afghanistan

At least 14 people were injured in the blast which happened when the troops were conducting a foot patrol in Kunduz city, in the province of the same name.

An Afghan interpreter working with the troops was among those killed, and two Germans were among the injured.

About 3,000 German troops are based in northern Afghanistan as part of the Nato forces in the country.

Witnesses say a suicide bomber on foot targeted the German patrol as they walked through a shopping district in the city.

"Suddenly we heard a big sound. We were frightened," Aziz, a shopkeeper, was quoted by Reuters as saying. "We saw very thick smoke and people rushing to escape."

German Chancellor Angela Merkel said: "These perfidious murders fill us all with disgust and horror."

She expressed her "deepest sympathies" to the relatives of the German and Afghan victims, but said such incidents would not deter Germany from its reconstruction mission.

US troops hurt

On 16 April, a Taleban suicide bomber attacked a group of policemen doing morning exercises in Kunduz, killing nine and injuring 25.

In a separate incident, four US troops were reportedly injured when their vehicle rolled down a steep slope after a failed suicide car bomb attack in Khost, in the south-east of the country.

A suicide bomber had driven into their convoy, but his explosives failed to go off, the BBC's Alastair Leithead in Kabul said.

Lengthy gun battle

And in the eastern province of Paktia, near the Pakistan border, coalition troops and Afghan security forces clashed with Taleban militants late on Friday in a gun battle which lasted several hours.

Afghan army officials said more than 60 insurgents were killed in the fighting, though this has not been verified. No coalition or government forces were reported injured.

Paktia province has been the scene of frequent violence involving the Taleban, the radical Islamist group toppled from power after the US-led invasion of Afghanistan in 2001.

The Taleban are threatening to increase their attacks following the killing of their top military commander Mullah Dadullah a week ago.

Dadullah was killed in an operation by the US-led coalition, supported by Isaf, in Helmand province.

Dadullah's name had been linked with the beheading of suspected spies, controlling the guerrilla war in Helmand province, dispatching suicide bombers and the kidnapping of Westerners.