A Houthi militant runs from a mosque where a suicide bomber blew himself up in Sanaa March 20, 2015.

Houthi fighters opposed to Yemen’s president seized parts of the country’s third largest city of Taez amid growing concern about a conflict diplomats say risks drawing in neighboring oil giant Saudi Arabia and its main regional rival Iran.

The U.N. Security Council was set to meet to discuss Yemen after President Abd Rabbu Mansour Hadi, a U.S. ally, accused the Iranian-allied Houthi militia of staging a coup against him and appealed to the United Nations for “urgent intervention”.

U.S. officials said Washington had evacuated its remaining personnel from Yemen, including about 100 special operations forces, because of worsening security, marking a setback in U.S. efforts against a powerful al Qaeda branch.

Conflict has been spreading across Yemen since last year when the Houthis seized the capital Sanaa and removed Hadi from effective control of the state, angering Gulf Arab states led by Saudi Arabia, the world’s top oil exporter, which regards the Shiite movement as a terrorist group.

The Houthis then advanced into Sunni Muslim areas, leading to clashes with local tribes and al Qaeda and energizing a southern separatist movement.

In Taez, located on a main road from the capital Sanaa to the country’s second city of Aden, residents said that Houthi militias took over the city’s military airport from local authorities late on Saturday.

Protests

The fighters also took control of a number of government buildings and a prison, they said.

The takeover of the airport happened without a struggle, but later eyewitnesses reported Houthi gunmen firing tear gas and shooting into the air to disperse protests by residents demonstrating against the presence of Houthi forces.

Eyewitnesses in the central province of Ibb described to Reuters seeing a column of dozens of tanks and military vehicles travelling from the Houthi-loyalist north on their way southward toward Taez, 150 kilometers northwest of Aden.

On Sunday, anti-aircraft guns opened fire at an unidentified plane flying over Hadi’s compound in Aden and appeared to force it away, witnesses said.

It was the third incident of its kind in four days, in which aircraft have flown over the compound, where Hadi is based, on one occasion dropping bombs without causing any casualties.

Aden’s governor Abdulaziz bin Habtoor has accused the Houthi movement of ordering the flights over Aden, an allegation the group, which controls much of the north, has yet to address.

The Houthis are allied with former president Ali Abdullah Saleh, who still has influence in the military despite having given up power in 2011 after mass protests against his rule. The Yemeni army has varied loyalties, with most units being controlled by the Houthis or Saleh, while some are loyal to Hadi.

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