Two Yemeni soldiers were killed on Thursday as they deployed to police a truce between Shiite rebels and hardline Sunnis in the north, a military official said.

"A mine exploded as a military vehicle passed by, killing one soldier instantly and grievously wounding another who died later," the source told AFP.

The explosion came as the soldiers were moving in to place themselves between Zaidi Shiite rebels and Salafist fighters in the town of Dammaj, the official said.

The deployment was taking place under a ceasefire obtained by the presidency and parliament to separate the two groups that have battled sporadically since the end of last month.

Fighting has centred on a Salafist mosque and Koranic school in Dammaj that has been besieged by the rebels, known as Huthis after their leading family.

Huthis have been battling the central government for nearly a decade in remote Saada province, but the latest fighting between the rebels and the Salafists has given an added sectarian dimension to the clashes.

Under the ceasefire -- the third since the fighting erupted -- supplies would be sent in to the surrounded Salafists, one mediator, MP Mohammed Ali Mekhlafi, said.

UN special envoy Jamal Benomar has warned that the fighting in Dammaj "threatens the security of Yemen".