* Death would be blow to al Qaeda's regional leadership
* Killing raises fears for fate of Western hostages
Al Qaeda's senior field commander in the Sahara, Abdelhamid Abou Zeid, has probably been killed in Mali, the head of France's joint chiefs of staff said on Monday.
Edouard Guillaud's remarks are the first indication from the French government that Abou Zeid died in fighting in the rugged north of Mali.
Asked on Europe 1 radio whether he had been killed, Guillaud said: "It is probable, but only probable. We don't have any certainty for the moment, (but) it would be good news."
Guillaud said that Abou Zeid's death could not be confirmed because his body had not been recovered.
Chad's army, which is fighting alongside French forces in northern Mali, said last week that it killed Abou Zeid and another al Qaeda commander in the area, Mokhtar Belmokhtar.
Guillaud said he was "extremely cautious" about reports of Belmokhtar's death, noting that some militant websites had said the al Qaeda commander behind January's mass hostage-taking in Algeria was still alive.
Abou Zeid is regarded as one of AQIM's most ruthless operators, responsible for the kidnapping of more than 20 Western hostages since 2008. He is believed to have killed British hostage Edwin Dyer in 2009 and 78-year-old Frenchman Michel Germaneau in 2010.
While his killing would deal a serious blow to al Qaeda's leadership in the region, it also raises questions about the fate of seven French hostages thought to be held in northern Mali.
After a seven-week-old campaign, French, Chadian and Malian troops have pushed Qaeda-linked fighters, who had threatened to take over Mali, back to their mountain and desert hideouts.
Guillaud said French forces had found some 50 supply caches and around 10 workshops for making bombs that could be used well outside of the immediate region.
"On the ground we are finding literally an industrialisation of terrorism," he said.