Ban warned that "Yemen is collapsing before our eyes" and the UN could not stand by and watch. The secretary-general addressed the Security Council Thursday before a briefing by the UN's Yemen envoy, Jamal Benomar, who has led efforts to get the Houthis to restore political stability in Yemen.

"The country will descend into civil war and disintegration," Benomar told the council by video link from Sanaa, the capital, on Thursday, "or the country will find a way to put the transition back on track."

Ban called for Houthis to free President Abedrabbo Mansour Hadi and Prime Minister Khaled Bahah, whom they deposed last week and have since held under de facto house arrest. Speaking from Yemen, Benomar said he remained "in the middle of delicate negotiations" daily with all parties involved.

'Take further steps'

Over the weekend, Ban called for the Houthis to fully restore the presidential powers Hadi had received in 2012 as the lone candidate to replace the autocrat Ali Abdullah Saleh. Saleh had fallen from power after a series of protests as part of the multinational Arab revolution, which began in Tunisia at the end of 2010. Ban made his demand following talks with King Salman, who came into his throne as monarch of Sunni Saudi Arabia when his brother died in late January. Saudi Arabia has described the ascendance of the Houthis as a coup.

Last week, the UN Security Council threatened to "take further steps" if negotiations to end the crisis failed - a veiled reference to possible sanctions.

Yemen, a key US ally in the fight against al Qaeda in the Arabian Peninsula, has remained in turmoil since the Houthis seized Sanaa in September. On Wednesday, the United States, Britain and France rushed to close their embassies over security fears, with US staff destroying top-secret documents and sensitive equipment before pulling out. The Houthis quickly helped themselves to weapons left behind after US staff evacuated.

On Thursday, an al Qaeda offshoot in Yemen claimed to have seized a government army base in the southern part of the volatile country (pictured). Al Qaeda-linked Ansar al-Sharia (Partisans of Sharia) claimed in a Twitter statement that insurgents fully controlled the 19th Infantry Brigade in the southern province of Shabwa after an attack.

The militant Sunni group accused the Yemeni army of alliance with Shiite Houthi forces, a sworn enemy of al Qaeda. Yemen's army released no immediate comment.

mkg/rc (Reuters, AFP, dpa, AP)