Al-Qaeda’s branch in Yemen says it has killed 12 Houthi fighters in the central city of Radaa, a claim denied by the Shia group, which continues to move southwards after its takeover of the capital Sanaa in September.

Al-Qaeda in the Arab Peninsula (AQAP) said on Twitter that it targeted a vehicle carrying Houthis in an attack that killed a dozen fighters on Saturday.

Al Jazeera's Hashem Ahelbarra, reporting from Sanaa, said the Houthis denied they had lost fighters in any attack.

"They did state that they have control over most of the Radaa province and that they are expanding into the north of the country in order to fight al-Qaeda until the latter is defeated," he said.

He said concern has been mounting in Sanaa over Houthi fighters sending "massive reinforcement to the predominantly Sunni province of Maarib".

"Maarib is of crucial economic importance for the country since it is where most of the oil and gas installations are," he explained.

AQAP has been trying to persuade Sunni tribes to fight alongside them against the Houthis, Al Jazeera's Ahelbarra said.

"This is countered by the Houthis' official line that AQAP is vying for the control of Maarib to claim that this is a divided country."

The central province was also the scene of unrest on Saturday with the Houthis surrounding the house of the governor, Soltan Alarada.

Alarada, a member of the conservative Sunni Islah party and a staunch critic of the Houthis, denounced the siege in an interview to Al Jazeera, but called for "calm" and "restoration of the rule of law".

The developments came as dozens of activists rallied in Sanaa demanding the withdrawal of the Houthi fighters from Yemeni cities and the release of imprisoned activists who participated in the 2011 popular protests.

A new government was sworn in earlier this month as part of a UN-brokered peace deal that was signed in September to end the violence, but peace in the Arabian Peninsula nation has proved elusive.