Clashes broke out in Yemen's second most populous city between tribes and security forces during protests demanding that President Ali Abdullah Saleh step down.
Activist Samir Ghaylan says forces from the Republican Guard, headed by the president's son, used excessive force against tribesmen and protesters in Taiz to deter demonstrations against Saleh's 33-year rule.
Also Friday, a roadside bomb blast seriously wounded a resident of Taiz, which is south of the capital, Sanaa.
Hundreds of thousands of people took to the streets in 16 other provinces to denounce Saleh on Friday. A smaller group of several thousand pro-Saleh supporters rallied in the capital.
Saleh remains in Saudi Arabia receiving medical treatment after a June blast on his compound in the capital.