ADEN — The United States said it had evacuated all its staff from Yemen, whose embattled president has appealed for “urgent intervention” by the UN Security Council as attacks by Iran-backed rebels bring his country nearer to civil war. Houthi rebels seized Yemen's third largest city of Taiz and its airport on Sunday as thousands took to the streets in protest. Yemeni anti-aircraft guns opened fire at an unidentified plane flying over President Abdrabbu Mansour Hadi's compound in the southern city of Aden on Sunday and appeared to force it away, witnesses said. “Due to the deteriorating security situation in Yemen, the US government has temporarily relocated its remaining personnel out of Yemen,” State Department spokesman Jeff Rathke said in a statement. The UN Security Council was holding an emergency meeting on Sunday following Hadi's appeal. In his letter to the Council, Hadi denounced “the criminal acts of the Huthi militias and their allies,” saying they “not only threaten peace in Yemen but the regional and international peace and security.” “I urge for your urgent intervention in all available means to stop this aggression that is aimed at undermining the legitimate authority, the fragmentation of Yemen and its peace and stability,” Hadi wrote. In Taiz, 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. 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 seeing a column of dozens of tanks and military vehicles traveling from the Houthi-loyalist north on their way southward toward Taiz, 150 km (200 miles) northwest of Aden. Security sources said Houthi militiamen were also patrolling parts of Taiz and had set up checkpoints in Raheda, some 80 km (50 miles) south of the city on the road to Aden. A military source said troops loyal to Hadi and southern paramilitary forces had, meanwhile, deployed in Lahj province, north of Aden, in anticipation of a possible advance by the Houthis. — Agencies