Around 10 civilians were killed as Shi'ite Muslim Houthi fighters backed by Yemeni government fire fought into strongholds of al Qaeda and its Sunni tribal allies in the centre of the country on Sunday, local tribesmen said.
They said the Yemeni army pounded fighters of al Qaeda's local wing, Ansar al-Sharia, and local tribes with air strikes, artillery and Katuysha rockets in al-Baydah province, about 160 km (100 miles) southeast of the capital Sanaa.
"Around 10 civilians were killed and a number were injured, including women and children," one tribal source said. "But because it is dark and due to the continuing clashes, we were unable to retrieve all the victims," he told Reuters, adding that dozens of families had fled the fighting.
There were no details of casualties among the fighters.
The northern-based Houthis established themselves as power brokers in Yemen last month by capturing Sanaa against scant resistance from the administration of President Abd Rabbu Mansour Hadi, angering al Qaeda and Sunni Muslim tribal allies.
Another tribal source said heavy fighting was underway in the Khobza area, another stronghold held by Ansar al-Sharia and its allies, in al-Baydah.
"The Houthis are advancing to control the rest of Qaifa (tribal) areas and the night could see even more violent confrontations," the tribal official, who declined to be named, told Reuters by telephone.
The Houthis, with Yemeni army backing, earlier battled their way to al-Manasseh, a small town regarded as the main Ansar al-Sharia stronghold in the area.
Tribal sources said the Ansar al-Sharia fighters withdrew to another district called Bakla, about 3 km (two miles) away.
Al Qaeda, which follows a hardline Sunni Muslim ideology, views the Houthis, who hail from the Zaydi branch of Shi'ite Islam, as heretics.
The Houthis began advancing into central and western Yemen this month after an al Qaeda suicide bomber killed at least 47 people, mostly members of the group, as they prepared to stage a rally in Sanaa earlier this month.
Fighting has flared up in several provinces, alarming neighbour Saudi Arabia, the world's biggest oil exporter.
Until now the Yemeni army had avoided supporting the Houthis in their advance on al Qaeda. But Hadi considers Al Qaeda in the Arabian Peninsula (AQAP) as the main threat facing the country.
One tribal leader said the Houthis exploited old rivalries between two wings of one of the main tribes in the area, the al-Dahab tribe, and managed to enter the area, which had long been the main stronghold of Ansar al-Sharia.
Houthi officials made no comment but the group's television station said Houthi fighters and their allies have "reached the home of the leader of the criminal gangs" in al-Manasseh, referring to Ansar al-Sharia.
A U.S. drone struck al Qaeda targets in al-Manasseh on Friday, killing at least three people, tribal sources said.
Local sources said on Sunday that Abdel-Ra'ouf al-Dahab, the local leader of Ansar al-Sharia, and a number of Saudi members of the group were killed in the strike. Officials could not confirm the report.