A roadside bomb hit a United Nations vehicle in southern Afghanistan Tuesday, killing four Nepalese security guards and an Afghan driver, a police official said.

Afghan police officers check a UN vehicle after it was hit by a roadside bomb in Kandahar City.
(Allauddin Khan/Associated Press)

The victims were travelling through Kandahar City in a grey vehicle with blue UN licence plates when the explosion hit, said Ahmad Jan Agha, a police officer at the scene.

Four Nepalese men working as UN security guards and their Afghan driver were killed in the blast, said Esmatullah Alizai, Kandahar's provincial police chief.

A UN spokesman in the capital, Kabul, confirmed there had been an incident involving a UN convoy in Kandahar, but provided no details.

Separately, an old artillery shell exploded outside a school compound in western Afghanistan, killing three children and wounding four others, an official said.

The blast occurred at a school which shares a compound with a military base in the city of Herat, said Noor Khan Nekzad, a spokesman for provincial police chief.

An initial investigation suggested that the blast was accidental and was set off by children playing near the buried device, Nekzad said.