Three Al-Qaeda suspects were killed on Sunday in a U.S. drone attack in eastern Yemen, a local tribal chief said. The suspects were driving in a vehicle transporting weapons in the Saeed district in the eastern Shabwa province when the drone killed them, Agence France-Presse quoted the chief as saying. Washington classifies Yemen-based Al Qaeda in the Arabian Peninsula (AQIP) as the most dangerous affiliate of the radical group. Elsewhere in Yemen, clashes between Houthi militias and pro-government forces in southern Yemen overnight left 21 dead, on the fourth week of a Saudi-led air campaign against insurgents, medics and local sources said Sunday. Ten Houthi militias and four members of the Popular Committees volunteer groups fighting on the side of President Abdrabbu Mansour Hadi were killed in pre-dawn clashes in the southwestern city of Taez, the sources said. The Popular Committees are fighting alongside the military's 35th armoured brigade which remains loyal to the exiled Hadi. They received air support from warplanes of the Saudi-led coalition, which bombed Houthi positions, according to witnesses. The rebels sent in reinforcements from the cities of Hodeida and Ibb to Taez. The city has become the scene of fierce clashes over the past week, after having been largely spared in fighting that has spread across several Yemeni provinces.