Chris Leggett taught in a poor district of Nouakchott
Al-Qaeda's North Africa branch has claimed responsibility for the killing of an American aid worker shot dead in Mauritania, al-Jazeera TV reports.
The Arab satellite channel said it had received an audio message in which the group said it had killed 39-year-old Christopher Leggett on Tuesday.
Al-Qaeda in the Islamic Maghreb said it had targeted Mr Leggett for allegedly spreading Christianity in the country.
Al-Jazeera said it could not verify the authenticity of the message.
"Two knights of the Islamic Maghreb succeeded Tuesday morning at 8 a.m. to kill the infidel American Christopher Leggett for his Christianising activities," the group was reported to have said.
Unidentified gunmen ran up to Mr Leggett in the Mauritanian capital, Nouakchott, on Tuesday and shot him several times, witnesses said.
Mr Leggett, who grew up in Cleveland, Tennessee, taught at a centre specialising in computer science and languages in a working-class neighbourhood of the city, the Associated Press reported.
Al-Qaeda in the Islamic Maghreb is most active in Algeria, where it grew out of the remnants of the country's Islamist insurgency.
The group has also been blamed for attacks in neighbouring countries such as Mali and Niger, including the killing of a British hostage in northern Mali earlier this month.
In Mauritania, the former government said the group killed four French tourists in December 2007 - an attack that prompted the cancellation of the Paris-Dakar car rally.
The authorities also blamed the group for attacking the Israeli embassy in the capital, Nouakchott, in February last year.