Thousands of Shia in Bahrain took to the streets south of the capital Manama to protest against what they called repression of the opposition, witnesses said.
They marched in the Shia area of Bilad al-Qadim on Friday, waving the flag of the Gulf state and chanting slogans calling for jailed members of the opposition to be released.
The opposition, led by the Shia Al-Wefaq movement, in a statement charged that the government had not implemented the recommendations of a commission of inquiry into violence in the spring of 2011.
The investigation concluded that excessive force had been used by security personnel in the Sunni-ruled kingdom against mostly Shia protesters.
Friday's statement deplored "the continuing arrests, political trial and discrimination" against the majority Shia community.
The judicial authorities have stepped up the number of trials of Shia charged with attacking the police.
In the latest case, an appeals court on Monday upheld jail terms of up to15 years for 17 Shias convicted of attacks on the police.
'89 killed in protests'
A Shia-led uprising to demand democratic reforms in Bahrain was crushed in March 2011.
King Hamad in August ordered stiffer penalties for "terror acts". These include a minimum 10-year jail term for an attempted bombing. If such attacks cause casualties, the sentence can be life imprisonment or the death penalty.
The authorities have also banned demonstrations in Manama.
Strategically located across the Gulf from Shia Iran, Bahrain is home to the US Navy's Fifth Fleet and is an offshore financial and services centre for its oil-rich Gulf Arab neighbours.
At least 89 people have been killed since the protests began, according to the International Federation for Human Rights.