Houthi rebel fighters have taken control of crucial installations in Taiz, Yemen’s third-largest city, including the international airport, security officials said on Sunday, in a provocative expansion of the seven-month rebel offensive that has moved the country closer to war.

The Houthis’ advance into the city, over the last several days, also put them more firmly on a path toward military confrontation with opposing troops loyal to President Abdu Rabbu Mansour Hadi, based in Aden, about 120 miles southeast of Taiz. A senior security official in Taiz said the Houthis were flying troops and military equipment into the city’s airport, bolstering claims they were preparing a broader offensive.

Yemen has been gripped by unusually deadly and widespread violence for almost a week, raising fears that the impoverished country is headed inexorably toward civil war. Diplomats have all but admitted failure in brokering negotiations to end the conflict, while opposing forces on the ground accelerate their preparations for battle.

Yemen’s powerful Al Qaeda affiliate has capitalized on the political chaos to carry out attacks on the security forces. Another group, which said it was affiliated with the Sunni extremist Islamic State group, claimed responsibility for suicide bombings at Zaydi Shiite mosques in the capital on Friday that killed more than 130 people, in one of Yemen’s deadliest sectarian attacks.

Amid collapsing security in the country, the United States, a strong backer of Mr. Hadi, withdrew its last remaining military advisers from Yemen over the last few days.

The takeover of Taiz came a day after Houthi leaders issued a call for a “general mobilization” of soldiers and civilian fighters. The statement was seen as a declaration of war against Mr. Hadi, who fled to Aden last month after the Houthis all but forced his government from power.

Mr. Hadi, who has declared himself Yemen’s legitimate leader, demanded in a televised speech Saturday that the Houthis quit the capital and withdraw their fighters from Yemen’s cities.

NY Times