Somali militants linked to al Qaeda said on Wednesday, January 16 they had sentenced a French agent to death several days after an attempt by French armed forces to rescue him failed, Reuters reported.

Al Shabaab said in a statement the decision to kill Denis Allex, held hostage in Somalia since 2009, was unanimous and followed three years of what it called "exhaustive attempts at negotiations" over his release.

"With the rescue attempt, France has voluntarily signed Allex's death warrant," the militants said in an emailed statement that was also posted on the group's official Twitter handle.

France's Chief of Defense Edouard Guillard, asked to react to the statement, told Europe 1 Radio that Allex was presumed dead.

"We have nothing since Friday's raid on Denis Allex being alive. We think he is likely dead," Guillard said.

It was not immediately clear whether the rebels were saying they had already killed Allex.

"It is the government of France ... which must bear full responsibility for the death of Allex," al Shabaab said.

Guillard said the militants were engaging in "media manipulation."