Protesters pray as Pearl Square is seen behind them in the Bahraini capital of Manama Feb 19, 2011. [Photo/Agencies]

MANAMA - Thousands of anti-government protesters camped overnight in a Manama square that has come to symbolise their cause and waited for talks on Sunday between the opposition and the Gulf state's crown prince.

Bahrain's opposition is expected to put demands to Crown Prince Sheikh Salman bin Hamad al-Khalifa, who is leading a national dialogue after days of unrest that has left six dead.

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On Saturday protesters swarmed back into Pearl square putting riot police to flight and confidently setting up camp for a protracted stay.

On orders from the crown prince, troops and armoured vehicles had withdrawn from the square, which they had taken over on Thursday after riot police staged a night-time attack on a sit-in by protesters, killing four people and wounding 231.

"All political parties in the country deserve a voice at the table," Crown Prince Salman told CNN of the dialogue, adding the king had appointed him to lead it and to build trust with all sides.

"I think there is a lot of anger, a lot of sadness, and on that note I would like to extend my condolences to all of the families who lost loved ones and all of those who have been injured. We are terribly sorry and this is a terrible tragedy for our nation," he said.

The crown prince said protesters would "absolutely" be allowed to stay in the square.

The crowds in Pearl square swelled into the thousands on Saturday, celebrating a triumph for the overwhelmingly Shi'ite protesters who took to the streets on Monday, inspired by latest revolts that toppled leaders in Egypt and Tunisia.

Shoes left behind by those who fled lie in the street after Bahrain's security forces fired tear gas at anti-government demonstrators as they marched from Salmaniya Hospital to Pearl Square in Manama Feb 19, 2011. [Photo/Agencies]

In addition to withdrawal of security forces, the main opposition demands are the release of political prisoners, resignation of the government and talks on a new constitution, said an opposition source, who asked not to be named.

Ibrahim Mattar, a former parliamentarian from the Shi'ite party Wefaq, had said earlier that a main demand of the opposition was that the government accept the idea of turning Bahrain into a constitutional monarchy.

The demands likely will be put on Sunday to Crown Prince Salman, seen as a reformist, the opposition source said. The government said dialogue had already begun.

"The two main players are Sheikh Ali Salman and Ibrahim Sharif," the source said. Sheikh Ali is the secretary general of Wefaq, whose members quit parliament over the crisis, while Sharif heads the secular Waad group that has not won seats in parliament.