The grenade and automatic rifle attack was the first to target Westerners in Mali with reports that the assailant shouted “Death to the whites!” on entering La Terrasse restaurant and that he targeted the French national.
The French victim has been identified as Fabine Guyomard, 30, a single man with no children who worked for a US company that builds luxury accommodation.
Belmokhtar’s group Al-Murabitoun claimed responsibility in an audio recording carried by Mauritanian news agency Al-Akbar.
It said that it was to avenge “the prophet who has been mocked and insulted by the infidel West” – an allusion to cartoons of the prophet, most recently by French satirical paper Charlie Hebdo – and the killing of Al-Murabitoun leader Ahmed el-Tilemsi by the French army in northern Mali in December.
Belmokhtar, who was reported to have been killed in 2013 by the Chadian army but appears to be still alive, split from Al-Qaeda in the Islamic Maghreb to form his own group and was responsible for the attack on Algeria’s In Amenas gas plant in which 38 hostages died.
Police released two Malians arrested after the attack, saying that they were not involved and were “not terrorists by bandits”.
Investigators are now searching for the gunman and an accomplice witnesses report seeing at the scene, as well as a four-wheel drive vehicle apparently used for the getaway.
The 10,000-strong UN force in Mali, Minusma, has said it has made investigators and crime scene experts available to the authorities.
Malian Prime Minister Modibo Keita and President Ibrahim Boubacar Keita visited the scene on Saturday and said the authorities must not themselves be deflected from negotiations with Tuareg rebels, who formed an alliance with Islamist groups to seize the north of the country but have now broken from them.