World Bulletin/News Desk

At least 15 people were killed in heavy fighting between Sunni Muslim tribesmen and Shi'ite Houthi rebels in central Yemen on Friday, increasing fears of outright sectarian warfare.

The Houthi rebels established themselves as Yemen's new powerbrokers last month, capturing Sanaa on Sept. 21 to little resistance from residents or from the weak administration of President Abd-Rabbu Mansour Hadi.

Their ascendance has angered al Qaeda, which views Shi'ites as heretics and Houthis as pawns of Iran. Last week, the Yemen-based al Qaeda in the Arabian Peninsula (AQAP) claimed a suicide bombing on a Houthi gathering that killed at least 47 people.

In Friday's fighting, medical sources said 15 people from both sides were killed on the outskirts and inside the city of Ibb, 150 km (90 miles) south of Sanaa.

The city of Ibb borders al-Bayda province, a bastion of AQAP. Al Qaeda said in a statement that its fighters stormed the town of Odein, near Ibb on Wednesday, killing three soldiers and holding it for nine hours before withdrawing.

Houthi fighters have been making advances outside of Sanaa in recent days, taking over cities and towns with the apparent agreement of the authorities there. At least 10 people were killed on Thursday in fighting between Houthi tribesmen and al Qaeda-linked militants.

In addition to the rise of AQAP, the Houthi takeover of Sanaa, Yemen, an impoverished country of 25 million people, faces a secessionist movement in the south, creating instability that has alarmed neighbouring Saudi Arabia, the world's top oil exporter, and other Gulf Arab states.

Western and Gulf Arab countries have supported a U.N.-backed political transition since 2012 led by Hadi and meant to shepherd the country to stability after decades of autocracy.