A roadside bomb killed five people in a U.N. vehicle in the southern Afghan province of Kandahar on Tuesday, the provincial police chief said.

Four of those killed in the blast were from Nepal, Esmatullah Alizai told Reuters near the scene of the attack.

"Four Nepalese and one Afghan have been killed," he said.

The blast happened on a main road near Kandahar city, where Taliban attacks have become increasingly common.

"There has been an incident in Kandahar in which a U.N. convoy was involved," said U.N. spokesman Adrian Edwards. "We're checking, trying to confirm details."

In a separate incident, a blast in a school compound killed two students in the western city of Herat, officials and witnesses said.