Yemeni security officials say fighting between Shiite rebels and their opponents has killed over 33 people in Taiz, Yemen's third-largest city.

The officials said Tuesday that 21 rebels, known as Houthis, died in airstrikes by a Saudi-led coalition that opposes them. Eight civilians died when their bus hit a land mine and four fighters from the anti-Houthi forces were killed in street clashes.

The officials are independent in the conflict that is roiling Yemen. They spoke on condition of anonymity because they aren't authorized to talk to journalists.

Yemen's fighting pits the Houthis and allied army units against forces loyal to the internationally recognized government as well as southern separatists and militants.

At least 2,615 civilians have died since the anti-Houthi air campaign began in March, according to the U.N.