Afghan authorities say back-to-back explosions have killed as many as eight civilians in the eastern province of Khost.

Officials say at least 40 people were hurt Monday in explosions outside the electric company headquarters in the provincial capital, Khost City.  

Witnesses say the first blast was small.  They say the second explosion was caused by a suicide bomber on a motorbike and was much greater in intensity.

It is not clear who was responsible for the attack, or who they were targeting.  

Also in Khost Monday, NATO says its troops shot and killed an Afghan civilian in his car.  The international force says the car failed to heed a warning to stop.

Hours earlier, the Taliban claimed responsibility for a suicide bombing that killed three Afghan soldiers in southern Kandahar province.

Authorities say five soldiers and two civilians were wounded when the bomber rammed a car into a military convoy.

In the nearby province of Nangarhar, an explosion went off at an ammunition storage area Monday, killing a child and wounding 20 others.  Authorities are investigating whether the explosion was an accident.

Afghan soldiers supported by international troops have been fighting the Taliban since 2001, when a U.S.-led invasion pushed the hardline Islamist group from power.

The U.S. has made Afghanistan its top military priority and is sending 21,000 more troops and trainers to the country.

Some information for this report was provided by AFP, AP and Reuters.