Yemen’s Shiite rebels issued a call to arms Saturday to battle forces loyal to the country’s embattled president as U.S. troops evac8uatedng a southern air base crucial to America’s drone strike program.

The turmoil comes as Yemen battles al-Qaida in the Arabian Peninsula, the target of the drone program, and faces a purported affiliate of the extremist Islamic State group that claimed responsibility for a series of suicide bombings killing at least 137 people Friday.

All these factors could push the Arab world’s most impoverished country, united only in the 1990s, back toward civil war.

“I hate to say this, but I’m hearing the loud and clear beating of the drums of war in Yemen,” Mohammed al-Basha, a spokesman for the Yemeni Embassy in Washington, D.C., wrote on Twitter.

The Shiite rebels, known as Houthis, swept into Yemen’s capital, Sanaa, in September and now control it and nine of the country’s 21 provinces. President Abed Rabbo Mansour Hadi, a one-time prisoner of the Houthis in his own home, escaped last month and installed himself in Aden, declaring it the temporary capital amid the Houthi insurrection.

Earlier Saturday, Hadi gave his first televised address since fleeing the capital, striking a defiant tone. He described the rebels’ rule as “a coup against constitutional legitimacy.” He also pledged to raise the Yemeni flag over the Maran mountains, a stronghold for the Houthis, members of the Shiite Zaydi sect that represents nearly 30 percent of Yemen’s population.

Hadi also said regional Shiite power Iran supported the Houthis, something the rebels deny. Sunni Gulf countries have lined up to support Hadi and have moved their embassies to Aden to back him against the rebels.

Almost immediately after Hadi’s speech, the Houthis issued a statement announcing their offensive against security and military institutions loyal to Hadi, calling it a battle against extremists.

“The council announces this decision to call the proud sons of the Yemeni people in all regions to unite and support and cooperate with the armed and security forces in confronting terrorist forces,” they said in the statement carried by the Houthi-controlled state news agency SABA.

Though seizing power in Sanaa and clashing with those protesting their power grab, the Houthis largely have avoided open warfare since beginning their campaign in September. Their statement Saturday immediately recalled the years of war fought in the country, once split between a Marxist south that once was a British colony and a northern republic.

Meanwhile Saturday, U.S. troops including Special Forces commandos were evacuating from the al-Annad air base in southern Yemen, Yemeni security and military officials said. The officials did not say whether the troops had left the country.

The air base, the country’s largest, was believed to have some 100 American troops stationed there. On Friday, al-Qaida militants seized control of the nearby southern provincial capital of al-Houta in the group’s most dramatic grab of territory in years.