Police in Saudi Arabia opened fire Thursday to disperse a protest in the Eastern Province, injuring at least one person.

The rare violence raised concern about a crackdown ahead of more planned protests after Friday prayers in different cities throughout the oil-rich kingdom, Washington Post reports:

Despite the ban and a warning that security forces will act against them, protesters demanding the release of political prisoners took to the streets for a second day in the eastern city of Qatif. Several hundred protesters, some wearing face masks to avoid being identified, marched after dark asking for “Freedom for prisoners.”

Police, who were lined up opposite the protesters, fired percussion bombs, followed by gunfire, causing the crowd to scatter, a witness said, speaking on condition of anonymity for fear of government retaliation.

The witness said at least one protester was injured and lifted by others to a car for treatment. It was not clear how the protester was injured.

Scores of protesters in Qatif had also marched in the city streets Wednesday night.