At least eight Yemeni soldiers and five militants were killed when Islamist gunmen attacked an army checkpoint in the central Maarib province on Tuesday, a local official said. In the southern city of Lawdar, where 57 people were killed on Monday in clashes between government forces and fighters from al Qaeda-linked group Ansar al-Sharia (Partisans of Islamic Law), fighting was intensifying, residents said. Two tribesmen fighting alongside government forces and six militants were killed, residents and security officials said. President Abd-Rabbu Mansour Hadi, who took over in February after a year of mass protests against his predecessor Ali Abdullah Saleh, is under pressure from Washington to fight his country's al Qaeda branch. On Tuesday, gunmen in vehicles fired on the army checkpoint in Abar, some 300 km (186 miles) east of the capital Sanaa, killing eight soldiers and wounding four before fleeing, a local official said. Five of the militants were also killed. The official, who spoke on condition of anonymity, blamed al Qaeda-linked militants for the attack , but it was not clear if they were part of Ansar al-Sharia. The group claimed on Monday it had captured a large cache of arms and ammunition, including four tanks and anti-aircraft guns during fighting with Yemeni troops in Lawdar. Residents said fighting intensified on Tuesday with warplanes bombing two sites held by the Islamist fighters 10 km (6.2 miles) west of Lawdar, destroying at least one of the tanks the group had seized a day earlier.