Mauritania has accused Islamic insurgents from Algeria of attacking a Mauritanian army base in the Sahara desert killing at least 15 soldiers.
Defence Minister Baba Ould Sidi said the gunmen were from the Salafist Group for Preaching and Combat (GSPC) - suspected of links to al-Qaeda.
He said 17 other soldiers were injured in an attack on Saturday, in the remote north-east near Algeria and Mali.
The United States warns the area is a training ground for Islamist recruits.
At least five attackers were killed in the attack, the minister said, adding that they took six military vehicles and burnt two others.
"They killed in cold blood the soldiers they had taken prisoner before fleeing," he told a news conference in the capital, Nouakchott.
Following the attack, the army was placed on full alert and reinforcements and reconnaissance aircraft were sent to the region.
In recent months the Mauritanian government has arrested about 50 people accused of links with al-Qaeda.
Critics accuse the government of using the US-led war on terror to crackdown on Islamic opponents.
Mauritania's President Maaouiya Ould Sid Ahmed Taya has angered Islamists by establishing links with Israel.
There have been three coup attempts since June 2003.