ADDIS ABABA, Dec 23 (Reuters) - Ethiopia said on Saturday an appeal to foreign Muslim fighters by Somalia's Islamists proved the "extremism" of the movement Addis Ababa accuses of being run by al Qaeda-linked militants. "If wishes were horses, the extremists in the Islamic Courts Union would have attacked Addis Ababa by now," Ambassador Solomon Abede, Foreign Ministry spokesman, told Reuters. "Their declaration appealing to foreign Muslim fighters to help in war against Ethiopia proves their extremist behaviour."