KABUL – A massive bomb blast triggered in central Afghanistan killed 25 people including primary school students Thursday, destroying shops and leaving pieces of the vehicle carrying the explosives more than a mile away.

The bomb was detonated in a timber truck overturned on the side of the road, killing 21 civilians and four policemen in Logar province, south of Kabul, ministry spokesman Zemerai Bashary said. At least nine of those killed were children from a nearby school, said Kaamaluddin Zadran, a provincial official.

Authorities said they suspected the truck may have been heading into Kabul with the explosives, but that it overturned on the main road between Logar province and the capital late Wednesday, provincial police chief Mustafa Khan said.

After police arrived to clear the road, militants apparently decided to blow up the truck, Khan said, adding that authorities believe the explosives were mixed with timber in the back of the vehicle and remotely detonated.

The power of the blast sent truck pieces flying more than a mile (2 kilometers) away, another police official said.

The blast occurred in Mohammad Agha district, close to shops that collect milk from farmers, said the second police official. He spoke on condition of anonymity because he was not authorized to speak to the media.

The explosion happened as thousands of U.S. Marines in southern Afghanistan are involved in the biggest American military offensive in country since the ouster of the Taliban from power in 2001.

In the southern province of Zabul, meanwhile, Afghan and coalition troops battled Taliban militants who attacked a government center in Suri district early Thursday. Fifteen insurgents were killed and another was detained, said provincial police chief Abdul Rehman Sarjang.

No casualties were sustained among Afghan and foreign troops, Sarjang said.

Southern Afghanistan is the center of the Taliban-led insurgency. The hard-line Islamist militia has made a violent comeback in recent years since the 2001 U.S. invasion.