Shiite militia in Yemen seized the airport in a key central city on Sunday as deteriorating security prompted Washington to evacuate personnel and the UN Security Council to call an emergency session.
The Security Council was to meet later on Sunday after President Abedrabbo Mansour Hadi called for "urgent intervention" amid mounting unrest, including suicide bombings claimed by the Islamic State group that killed 142 people in the capital Sanaa on Friday.
Impoverished but strategic Yemen has descended into chaos in recent months, with the Shiite militia, known as Huthis, seizing control of Sanaa and forcing Hadi to flee to the main southern city of Aden.
The Arabian Peninsula country is increasingly divided between a north controlled by the Huthis, who are allegedly backed by Iran, and a south dominated by Hadi's allies.
On Sunday the Huthis and their allies seized the airport in the city of Taez, which is just 180 kilometres (110 miles) north of Aden on the road to Sanaa and seen as a strategic entry point to Hadi's refuge.
Security sources told AFP some 300 men, including Huthi fighters dressed in military uniforms and allied forces, had deployed at the airport and reinforcements were arriving from Sanaa by air and land.
The forces allied with the Huthis included members of the former central security force, a unit seen as loyal to ex-president Ali Abdullah Saleh.
Saleh was forced from power in early 2012 after a year-long popular uprising and has been accused of working with the Huthis to restore his influence.
Security sources said Huthi militiamen were also patrolling parts of Taez and had set up checkpoints in Raheda, some 80 kilometers 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 Huthis.
Vow to fight Iran influence
Hadi, backed by Western and Gulf states as Yemen's legitimate ruler, has been struggling to reassert his authority since escaping house arrest in Sanaa last month and fleeing to Aden.
In a letter to the Security Council, he said the Huthis and their allies "not only threaten peace in Yemen but regional and international peace and security".
He called for "urgent intervention by all available means to stop this aggression that is aimed at undermining the legitimate authority, the fragmentation of Yemen and its peace and stability."
The country is increasingly divided along sectarian lines, with the Shiite militia facing resistance from Sunni tribesmen and Al-Qaeda in the Arabian Peninsula (AQAP), the powerful branch of the global jihadist network.
The Huthis were targeted on Friday by IS, who claimed responsibility for the series of devastating suicide bombings against mosques in Sanaa.
Yemen has long been a key US ally in the fight against Islamic extremism, allowing Washington to carry out drone strikes on AQAP on its territory.
But in statement on Saturday, Washington said it was evacuating its remaining personnel from the country.
"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.
The US would "continue to actively monitor terrorist threats emanating from Yemen and have capabilities postured in the area to address them," Rathke said.
Washington late Friday pulled out troops from the Al-Anad airbase in southern Yemen amid fighting between Yemeni security forces and Al-Qaeda militants nearby which left at least 29 dead.
Yemen has acknowledged that US personnel gathering intelligence for drone strikes on Al-Qaeda are deployed at Al-Anad. Hadi has been trying to cement his power base in Aden which he declared the temporary capital after he retracted a resignation tendered under Huthi pressure.
On Thursday, his forces overran the base of special forces in Aden after its commander refused Hadi's decision to remove him. On Saturday he pledged to fight Iranian influence in his country, accusing the Huthis of importing Tehran's ideology.
Hadi said he would ensure that "the Yemeni republic flag will fly on the Marran mountain in (the Huthi militia's northern stronghold) Saada, instead of the Iranian flag".
Track Latest News Live on NDTV.com and get news updates from India and around the world