Twenty Taliban were killed after a seven-hour gun battle with a police convoy in the western province of Farah, interior ministry spokesman Zemarai Bashary told AFP.

"Our police engaged the enemy with bravery and killed 20 Taliban," he said, adding that three policemen were also injured during the fighting in the Dasht-i-Bakwa area.

Officials say insurgents have infiltrated Farah province bordering Iran after being defeated by foreign and Afghan troops in the troubled southern provinces last year.

Separately, US-led troops and aircraft attacked a group of militants preparing to launch a rocket attack in the eastern province of Paktika and killed up to seven rebels Friday, the coalition said in a statement.

The attack happened in Bermel district, a township on the Pakistani border.

"Coalition forces spotted a group setting up rockets and engaged the group with indirect fire... Coalition aircraft dropped two munitions on the site and then another one on five personnel moving into a wadi (valley)," it said.

"A ground patrol moved to the site and confirmed that two were killed and another five are suspected dead," the statement said.

A militant was killed and another was injured late Thursday when a bomb they were planting on a roadside went off prematurely in eastern Kunar province, a police official said.

The injured man was detained by US-led troops for questioning, the official told AFP on condition of anonymity.