Yemen is nearing "the edge of civil war", the UN envoy to the country warned as the Security Council voiced unanimous support for its embattled leader and Shiite militia seized the airport in a key city.
The impoverished country has descended into chaos in recent months, with the militia, known as Huthis seizing control of capital Sanaa and forcing President Abedrabbo Mansour Hadi to flee to the main southern city of Aden.
The UN Security Council held an emergency session Sunday as unrest mounted, including suicide bombings claimed by the Islamic State group that killed 142 people in Sanaa on Friday.
Its 15 members voiced their unanimous support for Hadi, who called in a letter to the council for "urgent intervention by all available means".
"(Recent events) seem to be leading Yemen to the edge of a civil war," UN envoy Jamal Benomar told the meeting on Sunday by video link from Qatar, warning that without immediate action "the country will slide further into further violence and dislocation".
In a letter to the council, Hadi said the Huthis and their allies were threatening security in Yemen, the region and beyond.
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".
Hadi has been struggling to reassert his authority and cement his power base in Aden, which he declared the temporary capital after retracting a resignation tendered under Huthi pressure.
A statement from the Security Council said it "reaffirms its strong commitment to the unity, sovereignty, independence and territorial integrity of Yemen, and its commitment to stand by the people of Yemen".
The council "supports the legitimacy" of Hadi, it added while denouncing the "unilateral" actions by the Huthis and threatening unspecified measures against the militia unless it cedes control of Sanaa and other regions.
- Militia leader urges Yemenis to mobilise -
On Sunday, the Huthis and their allies seized the airport in 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 southern refuge.
Security sources told AFP that some 300 men, including Huthi fighters and allied forces, had deployed at the airport and reinforcements were arriving from Sanaa by air and land.
Meanwhile militia leader Abdulmalik al-Huthi urged Yemenis to mobilise and join his militia for an offensive against IS and Al-Qaeda in the south of the impoverished country.
"Al-Qaeda and Daesh must not be allowed to find refuge in any region" in Yemen, he said, using the Arabic acronym for the Islamic State group, which claimed responsibility for bombings of Huthi mosques on Friday that killed more than 140 people.
Speaking on television, he also dismissed Hadi as "a puppet in the hands of forces of evil, led by the United States", which he accuses of plotting against Yemen with funds from Saudi Arabia and Qatar.
Huthi also threatened to withdraw from UN-brokered dialogue between Yemen's many rival groups, implicitly rejecting a Saudi offer to host talks.
"Dialogue cannot go on for ever. It's a charade," he said.
The forces allied with the Huthis include 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 some 80 kilometres south of the city on the road to Aden.
A military source said troops loyal to Hadi and southern paramilitary forces had deployed in Lahj province north of Aden, in anticipation of a possible Huthi advance.
Huthi militiamen killed one protester in Taez when they fired on thousands of people demanding that the rebels withdraw, activists said.
And six tribesmen were killed in Qania, in Marib province, in a clash with Huthis advancing towards the eastern province, a tribal source said. The source claimed that 30 militiamen were killed. AFP could not verify the death tolls.
- Washington evacuates personnel -
Yemen, a long-time US ally which borders Saudi Arabia, is increasingly divided between a north controlled by the Huthis, who are allegedly backed by Iran, and a south dominated by Hadi supporters.
The Security Council statement also urged Sunday against any foreign interference, in an implicit reference to Iran's alleged support for the Huthis.
The Huthis also face resistance from Al-Qaeda in the Arabian Peninsula, considered by Washington to be the most dangerous branch of the jihadi network.
Washington announced Saturday it was evacuating its remaining personnel, underlining fears in the West of growing instability.
Washington would "continue to actively monitor terrorist threats emanating from Yemen and have capabilities postured in the area to address them", a State Department spokesman said.