Afghan officials say 10 young girls died in an explosion as they were collecting firewood Monday in eastern Afghanistan.

Authorities say they believe the blast came from an old landmine, one of many that are hidden in fields and rural areas across the country after decades of war. But the area near Pakistan is in a volatile part of Nangarhar province, where Taliban militants are active and could have planted such a device.

General John Allen, the commander of U.S. forces in Afghanistan, offered his condolences to the families, and said Afghanistan has become “one of the most heavily mined countries on Earth.”

Allen said “the tragic and cruel fact” about landmines is that “they do not discriminate.”

In separate violence, police say a suicide car bomber in the capital, Kabul, killed two Afghan workers and wounded at least a dozen other people at a compound owned by a U.S. military contractor.

The Taliban claimed responsibility, saying the contractor was involved in security. The company Contrack is involved in building aircraft runways and ammunition storage systems for military bases around Afghanistan.