KABUL, Sept 29 (Reuters) - A NATO soldier and an Afghan policeman were killed in an "altercation" after a joint patrol had detained seven civilians and brought them to a police station in eastern Afghanistan, the alliance said on Monday.

The deaths highlight the sometimes testy relations between Afghan security forces and their foreign mentors as they are engaged in a virulent Taliban insurgency that analysts say has grown in both scale and scope during the last year.

Afghan police and troops from the International Security Assistance Force (ISAF) were on a joint patrol in the eastern province of Paktia close to the Pakistani border on Sunday when they were hit by an improvised explosive device, a joint statement by ISAF and the Afghan Interior Ministy said.

Insurgents then engaged the patrol with small arms fire, it said. Later seven civilians were detained after testing positive for having explosive residues and taken to the Afghan police station at the district centre in the town of Jaji.

"While at the district centre, there was an altercation during which an ANP officer and one ISAF soldier were killed," the statement said.

ISAF spokesmen declined to elaborate on how the dispute began or who it was between, but Afghan media said the policeman opened fire on the troops who then fired back.

The vast majority of ISAF troops in eastern Afghanistan are American.

Some 3,000 people, at least 1,000 of them civilians, have been killed in Afghanistan this year, the bloodiest since U.S.-led and Afghan forces overthrew the Taliban in the wake of the Sept. 11, 2001 attacks on the United States. (Writing by Jon Hemming; Editing Valerie Lee)

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