Nine students were killed by a blast at a mobile popcorn stall near a school in eastern Afghanistan on Monday, an official said.

There were conflicting reports about the cause, with some saying the stall's gas cylinder had exploded while others suggested an old mortar bomb offered by a customer as payment had detonated.

Nangarhar province information official Qari Noor Mohammad Hanif told AFP the popcorn seller also died, and at least four more people were taken to hospital with burns.

Aqil Jan Ezzam, a spokesman for the interior ministry in the capital Kabul, said nine students were killed, blaming the incident on the gas cylinder.