Opposition leaders reported that 35 protesters were injured, three critically, and the government said several police officers were hurt.
The protests could derail negotiations that began after a regional force led by Saudi Arabia suppressed a Shiite-led uprising against the Sunni monarchy, The New York Times reported Thursday..
More than 30 people died during the conflict two years ago while hundreds were injured and thousands arrested, the BBC reported.
King Hamad has accepted the findings of an independent commission that said excessive force was used in putting down political dissent and has promised reforms.
Opposition groups charge Hamad has been slow to institute any changes and that he is not committed to serious reform.