At least 33 people were killed in a suicide bombing and gun attacks in central Yemen, tribal sources and medics said on Monday, as al Qaeda fighters seized a Yemeni city in a new challenge to the central government.

Violence has spread in Yemen since Shi’ite Muslim Houthis took over the capital, Sanaa, last month, threatening the stability of a country that borders on Saudi Arabia, the world’s biggest oil exporter.

Houthi forces have fanned out into central and western Yemen, posing a challenge to Sunni tribesmen and al Qaeda militants, who regard the Houthis as heretics. Fighting has flared in several provinces. […]