The Security Council was to meet later 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.
On Sunday the Huthis and their allies seized the airport in the city of Taez, which is just 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.
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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.
Security sources said Huthi militiamen were also patrolling parts of Taez and had set up checkpoints in Raheda, some 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 Huthis.