SANAA: Al-Qaeda-affiliated insurgents killed 18 Shiite Houthi rebels and seized an important city in central Yemen, tribal sources said on Monday, in a spread of sectarian conflict as central government authority has unraveled.

The northern-based Houthis established themselves as power brokers in Yemen last month by capturing the capital, Sanaa against scant resistance from the weak administration of President Abed Rabbo Mansour Hadi.

Tribal sources said that at least 10 Houthi fighters were killed when Al-Qaeda-linked Ansar Al-Sharia fighters shelled a house in the town of Radda in Al-Bayda province on Sunday night. Eight more Houthi fighters were killed in clashes on the outskirts of Radda, they said.

Ansar Al-Sharia said in a report from the Al-Orsh area in Al-Bayda that “dozens of Houthis” have been killed or wounded in battles since Sunday evening. “The battles are continuing until this moment,” the report added. There was no immediate word on casualties from Ansar.

Radda, with a population of 60,000, has long been a stronghold of Ansar, which includes many fighters from local tribes who are up in arms over the new presence of Houthi rebels in the mainly Sunni-populated region.