Al-Murabitoun was born of the fusion of Belmokhtar's al-Qaeda breakaway group "Signatories in Blood" and MUJAO, one of the jihadist groups that seized northern Mali in early 2012.
In an audio recording broadcast by Qatar-based al-Jazeera network yesterday, the group claimed yesterday's attack on the Radisson Blu hotel in Mali's capital Bamako, in which 27 people died.
"We the Murabitoun, with the participation of our brothers from al-Qaeda in the Islam Maghreb, claim the hostage-taking operation at the Radisson hotel," said a man's voice.
Belmokhtar, a former leader of al-Qaeda in the Islamic Maghreb, has on several occasions been declared dead, notably in last June and in April 2013, but his death was denied.
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An audio recording attributed to another leading member of al-Murabitoun in May pledged allegiance to the Islamic State jihadist organisation.
But Belmokhtar, nicknamed variously as "The Uncatchable" and "Mr Marlboro", reportedly quickly distanced himself from the declaration, vowing allegiance to IS's jihadist rival al-Qaeda in what was seen as a sign of a power struggle.
MUJAO is one of the al-Qaeda-linked groups which controlled northern Mali for nearly a year, between spring 2012 and the beginning of 2013. They were largely driven out by French forces.
On May 23 2013, a double suicide attack left 25 dead, mainly soldiers, in northern Niger. The attacks were claimed by "Signatories in Blood" and "MUJAO".
Three months later the two groups announced they were merging.
Al-Murabitoun has already claimed responsibility for the first attack on Westerners in the Malian capital on March 7.
The group claimed also an April 15 suicide attack against Niger's contingent at a UN base in the north and a July 14, 2014 suicide attack in the northern city of Gao, in which a French soldier was killed.
In Burkina Faso, a country previously spared by hostage-takings and terror attacks, the group claimed the abduction in April of a Romanian who was responsible for security in a mine in the north.