Seven civilians have been killed and nine others injured after a bus hit a roadside mine in eastern Afghanistan.

The explosion happened in Sabari district of the Khost province early on Wednesday on a road also used by foreign and Afghan troops, Abdul Qajum Bakizoy, the local police chief, said.

Bakizoy blamed Taliban fighters for laying the mine.

The province had witnessed frequent clashes between security forces and anti-government fighters in the past.

Taliban fighters and other groups regularly use roadside bombs in their attacks against Afghan and foreign troops, but the majority of the victims in such attacks have been civilian.

Nato says the number of roadside bombings rose by more than 30 per cent in 2008.

Nearly 2,200 civilians were killed in Afghanistan in 2008, the United Nations says. About 5,000 fighters were killed during the same year, according to military estimates.

Barack Obama, the US president, has ordered 17,000 more US troops for Afghanistan, where there are already about 75,000 soldiers under US and Nato command.