BERLIN, Aug 29 (Reuters) - Three civilians were killed in Afghanistan when a group of security forces including German soldiers opened fire at a checkpoint, Germany's defence ministry said on Friday.

The incident occurred outside the city of Kunduz on Thursday, when two cars ignored officials' calls to stop, defence ministry spokesman Thomas Raabe told a regular news conference.

Raabe said the checkpoint had been manned by Afghan police and German soldiers stationed in Afghanistan as part of a NATO mission. He declined to give further details.

NATO forces have been fighting a fierce insurgency by Taliban militants since 2005 and Berlin has come under pressure from NATO allies to increase its troop levels and transfer soldiers to the more dangerous south of the country.

Polls show a majority of Germans oppose having German troops in Afghanistan, and the civilian deaths could fan debate about the mission just weeks before parliament is expected to vote on increasing troop numbers.

Under a mandate that is due to expire in October, Berlin can send up to 3,500 soldiers.

Twelve German soldiers have been killed in attacks in Afghanistan since early 2002 -- including one this week -- while 16 more have died in accidents or from other causes.

The issue of civilian casualties has driven a rift between the Afghan government and its NATO backers. The United Nations said on Tuesday it had found convincing evidence that 90 Afghan civilians, most of them children, were killed in air strikes by U.S.-led coalition forces in western Afghanistan last week. (Reporting by Kerstin Gehmlich; Editing by Caroline Drees)

AlertNet news is provided by