Several thousand people have held a protest outside the United Nations' offices in Bahrain's capital, Manama.
The demonstrators chanted "Down, Down, Khalifa" - a reference to long-serving Prime Minister Sheikh Khalifa Bin Salman al-Khalifa, activists said.
They also carried banners urging the UN to "intervene to protect civilians".
Witnesses said that police allowed the peaceful demonstration to proceed without interference, while a police helicopter hovered overhead.
One activist told the BBC: "Today the police were good. They didn't close off roads, they didn't attack us as they usually do with tear gas and stun grenades."
Observers say the police might have behaved with restraint because of a rare public rebuke by the United States last week over police tactics and the beating of a well-known human rights activist, Nabeel Rajab.
The US state department said the facts of the case were in dispute, but that it was very concerned "about frequent reports of excessive force".
Bahrain's ruling Al Khalifa family are Sunni Muslim, while the majority of the Gulf state's population - and those attending anti-government protests - are Shia Muslim.
The prime minister has held his position for more than 40 years. He is the uncle of the king, Sheikh Hamad Bin Isa al-Khalifa, and is widely considered to be a hardliner.
Longstanding Shia resentment over discrimination in the kingdom helped trigger months of unrest last year.
Tuesday's rally outside the UN's offices was organised by several opposition political parties, including the main Shia movement, al-Wefaq, and the secular Waad party, which is headed by a Sunni, Ibrahim Sharif.
Mr Sharif is currently serving a five-year prison sentence for plotting to overthrow the state, a charge which independent observers have said is without any merit.
Al-Wefaq and Waad have refused to take part in national reconciliation discussions ordered by King Hamad in the wake of a damning report by a panel of international human rights experts in November.
The report, commissioned by the king, is seen as an attempt to defuse tensions between the government and predominantly Shia protesters that saw at least 35 people die.
The committee was chaired by a distinguished Egyptian human rights lawyer, Professor Cherif Bassiouni.
His report documented numerous and systematic human rights abuses by the government against its citizens, including excessive use of force by police and torture in custody.