Tens of thousands of supporters of Bahrain's Shiite-led Opposition poured into Manama's Pearl Square calling for the government's downfall in the largest rally in more than a week of protests.

The capital's streets were clogged on Tuesday as protesters marched from the Bahrain Mall to the square, the focal point of anti-regime demonstrations that have gripped the Gulf state since in February 14.

Those leading the protest carried a large banner reading, "The march of loyalty to martyrs" which bore the pictures of seven protesters killed by security forces.

Another poster strung from a bridge read in English, "No dialogue before the downfall of the ruling regime."

"The people want the fall of the regime," protesters chanted.

The widow of one of the victims read a statement outlining the Opposition's demands, which centre on the current government's resignation and the replacement of the ruling Sunni Khalifa dynasty with a constitutional monarchy.

The statement also demanded an immediate, "impartial" probe to identify and try those behind the killings and reiterated opposition calls for the formation of a "national salvation" government.

Meanwhile, Saudi Arabia's state news agency said embattled Bahraini King Hamad would head to Riyadh on Wednesday, on a visit that coincides with the expected return of Saudi King Abdullah from the United States.

The Bahraini monarch was the focus of the anger of thousands of Bahraini women, draped in black, who shouted: "May your hands be paralysed, Hamad."

"Down, down Khalifa," others chanted, condemning Prime Minister Sheikh Khalifa bin Salman, the uncle of King Hamad who has been in office since 1971 and who is widely despised by the Shiites.

"Our aim is either victory or martyrdom," said 20-year-old Mohammed, who refused to give his family name out of "fear of oppression."

Security forces have since been ordered to stay away from protesters who have daily crowded the square to demand the end of the Khalifa reign.

"We don't have a problem if elections bring a Sunni or a Shiite ruler," said 32-year-old protester Saeed.

"The most important thing is to have egalitarian distribution of wealth among both communities," added the father of two who earns 200 dinars ($530/391 euros) per month.

On Tuesday's rally marked the first protest officially called for by political associations since the protests began in response to calls by cyber activists inspired by uprisings in Tunisia and Egypt.

King Hamad has agreed to one of the opposition's demands, ordering the release of political prisoners and the end of trials against others.

The Islamic National Accord Association is the main Shiite formation and controls 18 seats in the 40-member parliament. Along with other opposition groups, it had demanded the prisoners' release as a precondition for considering a call for dialogue.

The Shiite opposition quit Parliament in protest at the killing of demonstrators and has demanded a constitutional monarchy and a peaceful alternation of power.

The political upheaval has forced the cancellation of next month's Bahrain formula one grand prix, and authorities fear the economy of the archipelago will be dented.

Bahrain has dwindling oil resources, while tourism from neighbouring Saudi Arabia is a significant source of revenues for many.

Meanwhile, amnesty international urged the Bahraini authorities to ensure the safety of people participating in peaceful protests.

But the United States on Tuesday welcomed peacemaking moves by Bahrain's monarchy.

"We view recent announcements to launch a national dialogue and the release of political prisoners as positive steps towards addressing the concerns of Bahraini citizens," state department spokesman Philip Crowley said.