Tribesmen loyal to the Shi'ite Houthi group attend a tribal gathering to show support to the group in Amran province north of the Yemeni capital Sanaa March 13, 2014, Fighters loyal to the Shi'ite tribe, who have repeatedly fought government forces since 2004, are trying to tighten their grip on the north as Yemen - home to one of al Qaeda's most active branches - moves towards a federal system that gives more power to regional authorities. REUTERS/Khaled Abdullah (YEMEN - Tags: POLITICS CIVIL UNREST)