Dec 21 (Reuters) - Hardline Islamist leader Sheikh Hassan Dahir Aweys on Thursday said his powerful military movement was at war with Ethiopian soldiers in Somalia. Witnesses says Ethiopian troops are helping the interim Somali government fight Aweys' Somalia Islamic Courts Council (SICC) near the government stronghold of Baidoa in the most sustained combat so far between the rival Somali factions. Here are key facts about the tense interplay of relations in the Horn of Africa, where Somalia has long been a battleground for various players' interests -- particularly Ethiopia's: * Ethiopia and Somalia have been rivals throughout history, and memories of the 1977-78 Ogaden war between the two are still fresh. Fought against a backdrop of shifting Cold War alliances, Ethiopia's army crushed Somali troops who tried to lay claim to the Ogaden region with the vision of recapturing ethnically Somali territories outside Somalia. Ethiopia had seized the Ogaden in the early 1900s in what Somalis viewed as a colonialist expansion by a Christian empire. * Ethiopia has not hesitated to send troops into Somalia to attack radical Somali Islamic movements, wary they could stir up trouble in the ethnic Somali regions on its side of the border. * In a way, the current fight is a repeat of history with the same players involved. Several times from 1992 to 1998, Ethiopian soldiers attacked members of al-Itihaad al-Islaami, a militant Somali group the United States has put on a list of organisations linked to terrorism. Aweys led its military wing at that time. Current interim President Abdullahi Yusuf, then a warlord with Ethiopian money behind him, led his militias against Aweys' al-Itihaad in that period. * A report to the United Nations on arms embargo violations says Eritrea has given weapons and training and sent about 2,000 troops to back the SICC, to frustrate the Ethiopian-allied interim government. Eritrea denies the charge, though makes no secret of its hatred of Ethiopia over their still-unresolved border dispute which led to a 1998-2000 war. * Military experts estimate Ethiopia has 15,000-20,000 troops inside Somalia. Addis Ababa says it only has a few hundred military trainers in Somalia. Nonetheless, witness reports for months have placed Ethiopian combat units inside Somalia, the latest of which said they were directly involved in fighting around Baidoa. Witnesses have also told Reuters they have seen an Ethiopian-flagged helicopter flying there.
