A day earlier, an official close to Hadi said he would not reconsider his resignation, despite pressure for him to do so by the Houthis, who he said are holding him "at gunpoint." They have kept him under de facto house arrest since earlier this month.

The Houthis control all major government buildings in Sanaa, as well as a number of key military facilities including the headquarters of the paramilitary special forces and air force.

A main movement representing southerners has already withdrawn from a U.N. sponsored dialogue with the Houthis, calling them 'absurd' and demanding that the rebels release Hadi and allow the country's parliament to convene normally.

Later in the day, armed Houthis, who have controlled Sanaa since September, broke up a protest against them at the city's main university, detaining several people. They hold around a dozen activists in the capital, after releasing some two dozen others in recent days.

In the southern city of Ibb, witnesses said two men on a motorcycle shot dead a Houthi leader, Abdullah al-Ayani. They declined to give their names for fear of retribution.

The governor of the southern port city of Aden said in a statement that he rejected any calls for separatism or sectarianism.