“Knights of the Islamic Maghreb, acting within one of the organisation’s brigades in Mauritania, struck the American infidel, Christopher Langis, known for his missionary activities,” Al-Qaeda said on Islamist websites.

“With grace from Allah, we were able to assassinate him, kill him, and purify the land of Mauritania from his criminal presence,” SITE quoted the statement as saying.

“May Allah bless these knights who are loyal to their Ummah (Islamic nation) and religion, who take vengeance for their innocent brothers, and who stand in the way of the crime of missionary in the land of Muslims.”

Al-Qaeda said Tuesday’s killing in Nouakchott was carried out at a time that “the despicable American bombs harvest our innocent Muslim brothers in Pakistan and Afghanistan.”

The man was shot several times in the head from close range after he resisted an apparent kidnap attempt, a witness told AFP, after the shooting outside a private language and computer school run by the American.

“A foreigner has been shot dead, apparently by youths who fled. We are investigating the case,” police said, while the interior ministry identified the man as Christopher Logest and said he also worked for a charity, Noura.

Al-Qaeda militants were blamed for the killing of four French tourists in Mauritania on December 24, 2007 that heightened concerns about extremist attacks.

A gun attack on the Israeli embassy on February 1, 2008 left three people wounded and was claimed by an Al-Qaeda offshoot.

Neighbouring Mali launched a military operation earlier this month to root out Al-Qaeda in the Islamic Maghreb fighters in the Sahel region bordering Algeria, Niger and Mauritania.

The North African branch of Al-Qaeda has sought to extend its range into nations on the southern edge of the Sahara and claimed several attacks in the region.