Witnesses say Saudi police opened fire Thursday in the oil-rich Eastern Province to disperse a crowd of several hundred Shi'ite activists demanding the release of prisoners.
Witnesses say up to four people were wounded in the shooting.
The police crackdown came in the wake a Saudi ban on protests enacted after several small groups of demonstrators gathered to demand change in the conservative kingdom.
In spite of the ban, activists have been using the Internet to urge Saudis to take to the streets Friday in the capital, Riyadh, for an anti-government "Day of Rage" rally. Organizers say they will use the rally to call for major political and social change.
The United States said Thursday it was closely monitoring the situation and reiterated its support for the right to peaceful assembly.
In February, Saudi King Abdullah announced a number of reforms, in an apparent effort to appease citizens in the wake of anti-government protests elsewhere in the Middle East.
The incentives included pay raises, increased spending on social programs and interest-free loans.
Some information for this report was provided by AP, AFP and Reuters.