Seven people are dead and dozens more are wounded after a car bomb exploded near a security building used by rebel Houthi fighters in central Yemen Friday.

A local official told Reuters the attack happened in the city of Bayhan in Shabwa province. The area has seen heavy fighting between Iran-allied Houthi fighters and local militiamen who have been supported by days of air strikes by several Arab nations, led by Saudi Arabia.   

Shiite rebels and allied military units in Yemen defied Saudi-led airstrikes to seize a provincial capital in a heavily Sunni tribal area Thursday. The Houthis overran the town of Ataq, capital of the oil-rich southeastern Shabwa province, after days of airstrikes and clashes with local Sunni tribes. The capture marked the rebels' first significant gain since the Saudi-led bombing began.

The Saudi-led coalition has imposed an air and sea blockade on Yemen and targeted both rebels and military units loyal to Iran, hoping to eventually allow Yemen's internationally recognized President Abed Rabbo Mansour Hadi to return to the country.

The coalition had hoped to keep the rebels out of the southern port city of Aden, which Hadi had declared his provisional capital after fleeing Sanaa earlier this year and before leaving the country last month. But there too the rebels and Saleh loyalists have advanced, sparking days of heavy clashes.

The conflict pits the Saudi-led Sunni Gulf countries against Shiite rival Iran. Tehran supports the Houthis and has provided humanitarian aid but both Iran and the rebels deny allegations that it has armed them. The growing regional involvement nevertheless risks transforming what until now has been a complex power struggle into a full-blown sectarian conflict like those raging in Syria and Iraq.

Meanwhile, humanitarian groups say they are running out of medical supplies to deal with the constant flow of casualties, particularly in Aden, where the fighting is most intense.

The groups have called for a temporary halt to the fighting to allow aid into Yemen. The World Health Organization said Wednesday that at least 643 civilians and combatants have been killed since March 19. At least 2,226 have been wounded, and another 100,000 have fled their homes.

The Associated Press contributed to this report.