An attack on Ethiopian troops in Somalia by the Islamist militant group al-Shabab has led to dozens of casualties, reports say.Ethiopian soldiers, and some Somali troops, were ambushed by the militants in Yurkut village in the central region of Geddo early on Saturday.Clashes continued for four hours.A BBC reporter in the capital Mogadishu says it is the most intense fighting involving Ethiopian troops since they entered the country last November.Al-Shabab claims to have killed 73 Ethiopians, while the Somali government says it in turn has killed 48 members of the militant group.Our correspondent reports that al-Shabab militants blocked roads around Yurkut before the ambush was carried out.Ethiopia's prime minister announced in January that his troops would be withdrawn from Somalia once African Union forces were in place.