BEIRUT, Lebanon  Saudi police officers opened fire at a protest march in a restive, oil-rich province on Thursday, wounding at least three people, according to witnesses and a Saudi government official. The crackdown came a day before a planned “day of rage” throughout the country that officials have said they will not tolerate.

Witnesses described the small protest march in the eastern city of Qatif as peaceful, but an Interior Ministry spokesman said demonstrators had attacked the police before the officers began firing, Reuters reported. The spokesman said that the police fired over the protesters’ heads, but that three people were injured in the melee, including a police officer.

Some residents agreed that the police had shot above people’s heads.

The clash with protesters in Qatif, located in a heavily Shiite region, underscored longstanding tensions in Saudi society: there is a sense among the Shiite minority that it is discriminated against by a government practicing a zealous form of Sunni orthodoxy. Mohammad Zaki al-Khabbaz, a human rights activist in Qatif who was reached by telephone, said that security forces fired tear gas and shot in the air trying to disperse the crowd.

He said an official at a nearby hospital reported that two protesters had been wounded, one in the leg and one in the arm. Mr. Khabbaz said he was told that they were not allowed to receive any visitors.