Somalia's most dangerous militant group says it has killed a French hostage that French military forces tried to rescue last weekend.

Al-Shabab said in a Twitter posting Thursday that the agent, codenamed Denis Allex, was executed Wednesday evening Somalia time.

French officials have said they believe Allex was killed the night of the raid. Allex, a French intelligence agent, was taken by the militants in July 2009 and had been held ever since.

A French raid Friday night and early Saturday failed to rescue him, and resulted in the deaths of two French troops and 17 Somalis, French officials say.