Three escaped jihadist prisoners were killed in Mauritania during an operation to recapture them, the government said on Saturday.
A police officer died, and a fourth prisoner was detained, officials said.
The operation took place overnight Friday in the rugged heartland mountainous area of Adrar, a security official said on condition of anonymity.
The four jihadists had escaped from a Nouakchott prison the previous Sunday.
Security forces "came under heavy fire which led them to engage in combat with the terrorist elements", the defence and interior ministries said.
The government hailed a "quality operation" carried out by security forces in this immense desert country of 4.5 million inhabitants.
No information had been released on the whereabouts of the jihadists in recent days, nor on how they reached the north.
But a security official said during the week that Ould Cheikh's "excessively dangerous" escape plan had been "very well organised and planned for a long time".
During the search for the fugitives, internet coverage has been disrupted all week across the country, NetBlocks, an organisation that monitors this activity around the world, told AFP, linking these disruptions to the hunt for them.
During the original escape, two guards were killed and two injured, said the interior ministry. The escape was a rare event in a nation spared the insurgency sweeping through the Sahel.
According to a military official, two of the prisoners had been sentenced to death, while the other two were awaiting trial for membership of a terrorist organisation.
One of the prisoners killed was Saleck Ould Cheikh, who had been on death row since 2011 for his part in a plot to assassinate former Mauritanian president Mohamed Ould Abdel Aziz, a military official confirmed.
The death penalty has not been enforced in Mauritania since 1987.
Ould Cheikh had already escaped prison in December 2015 before being arrested in Guinea Bissau and sent back to Mauritania after three weeks on the run.
The second prisoner on death row participated in attacks on the army in the north of the country in 2005, the military official said.
Mauritania has not experienced an attack on its soil since 2011, the result of security and political efforts made since the 2000s to curb the jihadist threat.
At the same time, jihadism was spreading to neighbouring Mali, then across the Sahel.
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 at the Pakistani hideout where former Al-Qaeda leader Osama bin Laden was killed, listing an attempt at rapprochement between the group and the Mauritanian government in 2010.
The government has denied this.
Mauritania was regularly targeted in the 2000s, including attacks and kidnappings.
Abdel Aziz, the former head of presidential security, came to power in a coup in 2008 and a year later was elected president.