Four jihadists have escaped from prison in Mauritaniafter a shootout left two guards dead, the interior ministry said Monday, a rare event in a nation spared the insurgency sweeping through the Sahel.

The National Guard has tightened its control over the prison and immediately started tracking down the fugitives," the ministry said in a statement to the official news agency. 

Two other guards were lightly wounded, it said. The identities of the escaped prisoners were not revealed.

According to a military official, two of the prisoners had been sentenced to death, while the others were awaiting trial for membership of a terrorist organisation. 

The official, asking not to be named, said their vehicle had been found northeast of the capital Nouakchott, site of the central prison.

The death penalty has not been enforced in Mauritania since 1987.

With a population of 4.5 million, Mauritania has been spared jihadist attacks since 2011, despite sharing a border with Mali, from where an insurgency that began in 2012 has spread across the region.

The absence of attacks has fuelled suggestions a secret non-aggression pact exists between Nouakchott and the jihadists.

Washington claimed to have found documents in 2011, in the Pakistani cache where former al-Qaeda leader Osama bin Laden was killed, listing an attempt at rapprochement between the group and the Mauritanian government in 2010.