Dilemma for rulers

"The question is whether they will be able to implement general reform, limiting the power of the king and so on. If they do that, in the long term, they are putting their own dominance and Sunni dominance at risk," Riana said, adding the authorities had long experience of dealing with unrest.

Health Minister Hamer said three people had been killed and 231 hurt in the police operation, and 36 people were still receiving hospital treatment.

"It is most unfortunate," he told Reuters at the bedside of a doctor badly hurt during the clash.

Opposition MP Mattar said later a fourth person had died of his injuries.

"He just died now, 20-30 minutes ago. He had wounds in the leg," he told Reuters, adding that it was not clear whether the man was injured in Pearl Square or in later clashes elsewhere.

The economic effects of the unrest are being felt, the King having already paid out generous allowances to families in an attempt to appease the population. Fitch ratings agency warned it might downgrade Bahrain's credit ratings in a few months.

A statement from Bahrain's defense forces, quoted by the Qatar news agency, said about 50 security force members had been wounded by demonstrators using "swords, knives and daggers".

"Security forces had to fire teargas and stun grenades to avoid losses," the statement said, adding the military had deployed in Manama "under orders to take all necessary measure to preserve peace and stability for citizens and residents".

King Hamad bin Isa al-Khalifa offered condolences to relatives of two men killed earlier this week and promised to investigate. Thursday's deaths took the total this week to six.

The police raid was short and sharp. Within 20 minutes protesters had fled, leaving tents, blankets and rubbish behind them as teargas wafted through the air, a Reuters reporter said.

A teenager shepherded a sobbing woman into a car, saying she had been separated from her two-year-old daughter in the chaos.