In Yemen, about 100 armed fighters loyal to a tribal leader clashed with security forces on the northern outskirts of the capital, Sanaa.Tribal leaders said hundreds more are marching towards the city in support of their leader, Sheikh Sadeq al-Ahmar, who leads the powerful Hashid tribal federation. According to Aviation officials and passengers, flights have been suspended at Sanaa airport. Fresh battles took place overnight between supporters of Sheikh Ahmar and government forces in Sanaa's northern Hassaba neighbourhood. At least 39 people were killed in the city on Wednesday following the breakdown of a ceasefire at the weekend.Elsewhere in the country, government forces opened fire on protesters in the southern city of Taiz. At least 50 people have been killed in Taiz since Sunday, according to the United Nations.