The French army said Thursday it had killed a top jihadist commander in a military operation in northern Mali, describing it as a heavy blow to Islamists operating in West Africa.

French forces in the northern Gao region carried out an operation alongside Malian troops which led to the "neutralisation of about a dozen members of an armed terrorist group, including Ahmed el Tilemsi," said army spokesman Gilles Jaron.

Malian Defence Minister Ba N'Dao specified in a statement that "six other terrorists were killed and three taken prisoner" in the operation.

With a string of kidnappings of westerners and attacks under his belt, Tilemsi was described by a terrorism expert as a "big fish" and right-hand man of notorious Algerian jihadist Mokhtar Belmokhtar.

Tilemsi was the leader of Belmokhtar's Al-Murabitoun group in Mali and was earlier this year declared a "specially designated global terrorist" by the US State Department, which offered a $5-million (four-million-euro) reward for information leading to his capture.

"We've really hit Al-Murabitoun hard," said Jaron.

Tilemsi has a long history with jihadist groups operating in the Sahel region, having been a member of Al Qaeda in the Islamic Maghreb (AQIM) before becoming one of the founding members of the Movement for Unity and Jihad in West Africa (MUJAO), a splinter group aimed at spreading jihad throughout the region.

MUJAO was one of a number of Islamist groups that occupied northern Mali last year, imposing a brutal interpretation of Islamic sharia law characterised by amputations, beatings and executions, before being ousted by the French-led military intervention.

In August 2013, it merged with a group run by Belmokhtar to form Al-Murabitoun, which loosely translates as "the guardians" and claimed to seek revenge on France for its actions in Mali.

- 'A very valuable target' -

The one-eyed Islamist Belmokhtar split from AQIM in 2013 to form his own group and masterminded a deadly raid against Algeria's In Amenas gas plant in which 38 hostages were killed in a four-day siege.

Tilemsi "was a very valuable target. We had been tracking him for several days," a French government source told AFP.

Mauritanian terrorism expert Isselmou Ould Salihi told AFP that Tilemsi's death would "hit Belmokhtar hard because he was his right-hand man, a big fish whose death could have a fatal impact on local jihadism."

The government source said Tilemsi was one of the masterminds of the kidnapping of Gilberto Rodrigues Leal, whom MUJAO claimed to have killed last April.

According to the US State Department, Tilemsi also played a role in the kidnapping of two Frenchmen, Antoine de Leocour and Vincent Delory, in Niamey in January 2011 while part of AQIM.

The hostages were later found dead after a failed rescue attempt by the French military.

Tilemsi also took part in the October 2011 kidnapping of three aid workers in Algeria, which left two wounded by gunfire, the State Department said.

"The group we hit was known for ... preparing suicide attacks," said the army spokesman Jaron.

Tilemsi, 44, a married father-of-four, was described by Malian security sources as illiterate and having been radicalised at a young age.

France has kept 1,000 troops in northern Mali since operation Serval ousted the Islamist rebels in the region, as part of a wider counter-terrorism operation.

The new operation, nicknamed Barkhane, is taking place across Mauritania, Mali, Burkina Faso, Niger and Chad and involves a total 3,000 French troops.

Jaron said French troops had "neutralised about 50 terrorists and several tonnes of weapons" since Barkhane was launched in August.

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