Nato troops arrest Afghan police chief

But Afghan provincial officials have insisted that the man was not involved in the resistance and angry officials at the Interior Ministry, which oversees the police, charged that Western officials had kept them in the dark about the arrest.

Attaullah Wahab, the deputy police chief and security director in Kapisa province, was detained along with a bodyguard in a raid backed by helicopters while he was at home in the provincial capital of Mahmud-i-Raqi.

Nato did not identify the suspect, but it said that "joint Afghan-coalition forces" had arrested an Afghan national police commander on Friday for illegal activity and corruption in Kapisa and the Bagram district in neighbouring Parwan province.

Bagram is the site of the main US military base in the country.

The Western military alliance accused Mr Wahab of involvement in "the storage, distribution and installation of bombs" on roads surrounding Mahmud-i-Raqi as well as corruption related to road reconstruction.

Nato said in a statement that Mr Wahab "has been clearly linked to criminal activities, including a murder during the summer of 2009."

A policeman's starting salary is £80 a month and the Afghan national police force is believed to be riddled with corruption at every level.

On Friday, a police unit reportedly mistook a group of villagers gathering wood near the Pakistan border for guerillas and opened fire, killing seven civilians.

The commander of the border police of southern Afghanistan said that the shooting in Shorabak district was under investigation.

Elsewhere in the south, tens of thousands of civilians have begun to evacuate the town of Marjah, near Lashkar Gah, ahead of a much-hyped Nato offensive.

Operation Moshtarak will see Nato troops - backed by special forces, war planes, attack helicopters, tanks and drones - attack suspected guerilla bases.

Western military chiefs say that once the area around Marjah is "cleared," Afghan security forces will move in to bring security and stability.

US Second Marine Expeditionary Force commander Larry Nicholson said that the evacuation of most civilians would give commanders leeway to use air-to-ground missiles, declaring that he was "not looking for a fair fight."