ADEN, Yemen — This port city, perched on an extinct volcano protruding into the Arabian Sea on Yemen's far southern edge, has become perhaps the last refuge of the country's embattled president, and it feels like now all his enemies are bearing down on it. Driven out of the capital, Sanaa, by Shiite rebels who have taken over much of the north, President Abedrabbu Mansour Hadi and the remains of his government have made Aden their provisional capital. If they lose here, Hadi — the man the US had hoped would stabilize the chaotic nation and fight Al-Qaeda's powerful branch — likely will fall, plunging Yemen into a civil war. In his first speech since fleeing Sanaa, Hadi on Saturday denounced the rebel takeover as “a coup against constitutional legitimacy” and declared Aden the country's “temporary capital.” Army and police forces loyal to Hadi and their allied militiamen patrol Aden's streets and man checkpoints at key locations. Tanks guard roads leading to the city and children are largely staying home from school. “There are great fears that plans are underway for Aden to meet the same fate as Sanaa,” Nayef Al-Bakry, Aden's deputy governor, told The Associated Press. Early this week, Hadi's forces fended off an attempt by rebel police commandos to capture the airport. And on Sunday, the Shiite rebels, backed by rebel forces, seized Yemen's third largest city, Taiz, 140 kilometers (85 miles) to the northwest of Aden. Officials here fear it is a prelude to an attack on Aden. The takeover of Taiz, known as the “gateway to the south,” followed the arrival there two days ago of a column of 20 armored fighting vehicles and 30 truckloads of Shiite rebel fighters and pro-Saleh troops. Equally worrying, Al-Qaeda militants on Friday took a city on Aden's doorstep, Al-Houta, capital of neighboring Lahj province. Al-Qaeda fighters now have positions only 20 kilometers (12 miles) from Aden. The drama in the south is just one part of Yemen's turmoil. A new alarming sign came Friday when suicide bombers hit two mosques in Sanaa controlled by the Houthis, killing more than 130 people in a devastating attack that may signal the emergence of a new branch of the self-proclaimed Islamic State group. Hadi fled Sanaa last month after escaping house arrest under the Houthis, who took over the capital in September. Aden is Yemen's second most important city and the country's economic hub, and as long as Hadi was here he could reasonably claim to still be president. Moreover, he chose Aden because as a southerner he has considerable support in the region. Aden was the capital of an independent South Yemen for decades until unification in 1990. Today, secessionist sentiment remains strong — many pro-Hadi militiamen in the streets wave the red, white, black and blue flags of the former South Yemen. Billboards welcoming Hadi to the city hang on many streets, along with pro-Hadi graffiti on the walls. Since he arrived, Hadi has issued calls for volunteers to join the army, a move his camp depicts as an attempt to build a military that stands above tribal, personal or regional loyalties. So far an estimated 20,000 men in Aden alone have volunteered. — AP