MOGADISHU, Dec 7 (Reuters) - Somalia's powerful Islamist movement said U.N. endorsement of an African peacekeeping force in Somalia will "add fuel to the fire" in the Horn of Africa nation many fear is on the verge of all-out war. "The U.N. authorising new weapons is like adding fuel to the fire," Islamist spokesman Abdirahman Ali Mudey told Reuters. "We are disappointed that the U.N. passed this resolution. It is unfortunate to add more weapons while the weapons that caused havoc are still in Somalia."