SANAA, Yemen — A band of al-Qaida militants took full control on Monday of a town 100 miles south of the Yemeni capital Sanaa, overrunning army positions, storming the local prison and freeing at least 150 inmates.

The capture of the town of Radda expanded already significant territorial conquests by the militants, who have taken advantage of the weak central government and political turmoil roiling the nation for the past year during an anti-regime uprising inspired by Arab Spring revolts.