Yemen's Shia militia sent reinforcements south and clashed with local fighters on Monday after the United Nations warned the country is on the brink of a protracted civil war. Security sources said the militiamen, known as Huthis, had sent thousands of troops and clashed with Sunni tribes, with their sights set on the main southern city of Aden, where President Abedrabbo Mansour Hadi fled to from the capital last month.
The militia on Sunday seized the airport and a nearby military base in Taez, 180 kilometres (110 miles) north of Aden and seen as a strategic entry point to Hadi's southern refuge.
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.
Mounting unrest - including suicide bombings claimed by the Islamic State (IS) jihadist group that killed 142 people in the Huthi-controlled capital Sanaa on Friday - have raised international concerns and prompted an emergency session of the UN Security Council on Sunday.
Its 15 members voiced their unanimous support for Hadi, with UN envoy Jamal Benomar warning that without immediate action the country will slide into "further violence and dislocation".
"(Recent events) seem to be leading Yemen to the edge of a civil war," Benomar told the meeting by video link from Qatar, warning of a protracted crisis like "a Libya-Syria combined scenario".
The Huthis seized Sanaa in September and have been expanding their territory, clashing with Hadi loyalists, local tribes and Sunni Islamist groups including al Qaeda.
Since taking over Taez airport, the militia has pushed toward Aden, security sources said, although two convoys were repelled in overnight clashes with tribesmen. It was not immediately clear how many Huthis or tribesmen may have been killed or wounded in the clashes near Al-Abd, about 40 kilometres from Taez, and Al-Maqatara, 80 kilometres from the city.
The Huthis have also deployed some 5,000 militiamen and more than 80 tanks to an area of neighbouring Ibb province, 30 kilometres north-east of Taez, local and military sources said.