(ADEN, Yemen)—Yemen’s Shi’ite rebels issued a call to arms Saturday to battle forces loyal to the country’s embattled president, as U.S. troops evacuated a southern air base over al-Qaeda militants seizing a nearby city, authorities said. The call by the rebels, known as Houthis, for a general mobilization only increases the ongoing chaos in Yemen, which grew exponentially in September when the Shiite rebels stormed into the capital, Sanaa. In their statement, the rebels described their coming offensive against security and military institutions loyal to President Abed Rabbo Mansour Hadi as a battle against extremists. Their appeal came just minutes after Hadi gave a defiant speech challenging the Houthis, his first address broadcast to the public since fleeing Sanaa last month.