The armed Islamist groups who have occupied northern Mali, sharing out key towns, are all acting under the aegis of Al-Qaeda in the Islamic Maghreb (AQIM), according to regional security sources.

Northern Mali's main cities and administrative regions, Timbuktu, Kidal and Gao have been occupied by Ansar Dine (Defenders of Faith) and the Movement for Oneness and Jihad in West Africa (MUJAO) since late March.

But in each city, security experts say, it is the North African Al-Qaeda franchise which is pulling the strings.

"AQIM has a chameleon nature, always taking on the local colour so as not to rush, sub-contracting to local jihadists while remaining vigilant," said one security source, on condition of anonymity.

Another security source said: "They organise everything. Food, military training, intelligence, ideological training. Let us not be mistaken, the hundreds of youths being recruited in the name of MUJAO or Ansar Dine are really AQIM fighters."

AQIM stems from a group started in the late 1990s by radical Algerian Islamists, who in 2007 formally subscribed to Al-Qaeda's ideology.

The group benefits from its perfect knowledge of northern Mali and its vast desert terrain, where it has spun a tight network across tribal and business lines, supporting poor communities and protecting traffickers.

They have made millions of dollars from ransoms of European hostages.

MUJAO was the first of the two Islamist groups to become known when in October 2011 it claimed the kidnapping of three European hostages, describing itself as a splinter group from AQIM.

Made up mostly of Algerians and Sahrawi, MUJAO now holds the northern Mali town of Gao, having chased out Tuareg separatist rebels who initially spearheaded the occupation of the north.

The takeover took place in the chaos following a coup d'etat in Bamako on March 22.

Last week, MUJAO released the three hostages for a ransom of 15 million euros ($18 million) and the release of an Islamist who had been imprisoned in Mauritania, the group said.

Scores of young Africans were seen arriving in Gao by a reporter, to join two training camps for "military and religious training", according to the leader of the new Islamic police force.

Algerian jihadists move around town in powerful vehicles, and residents have reported seeing notorious AQIM leader Mokhtar Belmokhtar, known as "the uncatchable" living in the town.

"He is living here with his son Oussama, from a marriage with a Malian," said one resident, adding that the town had become his base.

Corroborating sources reported Belmokhtar had supported MUJAO during the ouster of the Tuareg rebels at the end of June.

In the fabled city of Timbuktu, hardline Ansar Dine shocked the world by destroying ancient World Heritage sites such as the shrines of ancient Muslim saints, which they say are idolatrous.

The group has also enforced strict sharia law, whipping unmarried couples, drinkers and smokers.

In this ancient desert crossroads Abou Zeid, one of AQIM's most radical leaders, is in charge, living in a palace built in the city by late Libyan leader Moamer Gathafi.

His deputy Oumar Ould Hamaha is one of Ansar Dine's leaders, and a key player in the Islamist operation in northern Mali, where he coordinates the activities of the various groups.

An ideologist and feared warlord, Ould Hamaha recently threatened to attack West African countries who send troops to northern Mali and those who support them, such as France.

Kidal is held by Ansar Dine leader Iyad Ag Ghaly, a renowned former Tuareg rebel who led a 1990-95 rebellion, later becoming a mediator in hostage cases and peace talks before becoming radicalised.

Ansar Dine has said its main goal is to impose sharia law in Mali.