KABUL, Afghanistan - Ten young girls were killed when a bomb exploded as they were gathering firewood outside their village in eastern Afghanistan on Monday morning, an official said.

It was not clear what triggered the explosion outside Dawlatzai village in Nangarhar province's Chaperhar district, said Mohammad Seddiq, the government administrator for the district. He spoke to The Associated Press by phone from the site of the blast.

The girls ranged in age from 9 to 13 years old and all came from different families, he said. Two others were seriously wounded and are in critical condition at a hospital, Seddiq said.

He could not say if the blast came from a newly planted bomb or from an unexploded mine - many of which are still found in fields and rural areas from decades of conflict in the country.

Police are scouring the area for clues as to what type of explosive went off, Seddiq said.