Somalia's Islamist rebel group al-Shabab says it has decided to kill a French hostage, days after France carried out an unsuccessful rescue operation and presumed the man dead.

In a statement Wednesday, the militants said they reached a unanimous decision to execute Denis Allex. He has been held since being kidnapped from a Mogadishu hotel in July 2009 and was last seen in a videotape in October.

Allex was part of a team helping to train Somali government troops to fight al-Shabab.

France tried to free Allex in a raid late Friday that left two French soldiers and 17 rebels dead.

The militants said after the raid that Allex was still alive, but they have not shown any proof.