Bahrain's streets were mostly empty after the bloody clampdown, but thousands defied authorities by marching in cities in Libya and Yemen as the wave of political unrest continued in the wake of uprisings that toppled leaders in Egypt and Tunisia.
The tiny kingdom of Bahrain is a key part of Washington's military counterbalance to Iran by hosting the U.S. Navy's 5th Fleet. Bahrain's rulers and their Arab allies depict any sign of unrest among their Shiite populations as a move by neighboring Shiite-majority Iran to expand its clout in the region.
While part of the recent revolt in the Arab world, the underlying tensions in Bahrain are decades old and pit the majority Shiites against the Sunni elite.
After allowing several days of rallies in the capital of Manama by disaffected Shiites, the island nation's Sunni rulers unleashed riot police who stormed a protest encampment in Pearl Square before dawn, firing tear gas, beating demonstrators or blasting them with shotgun sprays of birdshot. Along with two who died in clashes with police Monday, the new killings brought the death toll this week in Bahrain to seven.
The willingness to resort to violence against largely peaceful demonstrators was a sign of how deeply the monarchy fears the repercussions of a prolonged wave of protests.
In the government's first public comment on the crackdown, Foreign Minister Khalid Al Khalifa said it was necessary because the demonstrators were "polarizing the country" and pushing it to the "brink of the sectarian abyss."
Speaking to reporters after an emergency meeting with his Gulf counterparts in Manama to discuss the unrest, he called the violence "regrettable," said the deaths would be investigated and added that authorities chose to clear the square by force at 3 a.m. - when the fewest number of people would be in the square - "to minimize any possibility of casualties."
Many of the protesters were sleeping and said they received little warning of the assault.
In the wake of the bloodshed, angry demonstrators who milled around one hospital for treatment or to transport wounded friends and relatives chanted: "The regime must go!"
They stomped on and burned pictures of King Hamad bin Isa Al Khalifa outside the emergency ward at Salmaniya Medical Complex, the main hospital where most of the casualties were taken.
"We are even angrier now," shouted Makki Abu Taki, after viewing the birdshot-riddled body of his son in the hospital morgue. "They think they can clamp down on us, but they have made us angrier. We will take to the streets in larger numbers and honor our martyrs. The time for Al Khalifa has ended."
The Obama administration expressed alarm over the violent crackdown. Secretary of State Hillary Rodham Clinton called the foreign minister to register Washington's "deep concern" and urge restraint. Similar criticism came from Britain and the European Union, and Human Rights Watch urged Bahraini authorities to order security forces to stop attacks on peaceful protesters.
U.S. Defense Secretary Robert Gates said the U.S. has been encouraging reforms in the region for some time.
"The truth is I think the U.S. has consistently - primarily privately, but also publicly - encouraged these regimes for years to undertake political and economic reforms because the pressures were building," Gates told the Senate Armed Services Committee. "And now they need to move on with it and there is an urgency to this."
Analysts said the wave of unrest has so concerned leaders in the Gulf that they are willing to risk bloodshed.
"It was one thing when it was happening in Tunisia and Egypt and another when it arrives on their doorstep," said Toby Jones, an expert on Bahrain at Rutgers University. "The (Gulf rulers) are closing ranks now and showing how they are prepared to deal with challenges to their power. Their first instinct is to act quickly. It may be messy, but they don't want this to linger.
"They see that (if) it can happen in Bahrain, it could happen anywhere - something that was unthinkable just weeks ago," Jones added.
The protesters have two main objectives: force the ruling Sunni monarchy to give up its control over top government posts and all critical decisions, and address deep grievances held by the country's majority Shiites who make up 70 percent of Bahrain's 500,000 citizens but claim they face systematic discrimination and poverty and are effectively blocked from key roles in public service and the military.
The protests began with calls for the country's Sunni monarchy to loosen its grip but the demands have steadily grown bolder. Many protesters called for the government to provide more jobs and better housing, free all political detainees and abolish the system that offers Bahraini citizenship to Sunnis from around the Middle East.
Increasingly, protesters also chanted slogans to wipe away the entire ruling dynasty that has led Bahrain for more than 200 years and is firmly backed by the Sunni sheiks and monarchs across the Gulf.
Shiites have clashed with police before in protests over their complaints. But the growing numbers of Sunnis joining the latest protests have come as a surprise to authorities, said Simon Henderson, a Gulf specialist at the Washington Institute for Near East Policy.
"The Sunnis seem to increasingly dislike what is a very paternalistic government," he said, adding that the crackdown was "symptomatic" of Gulf nations' response to crises. "As far as the Gulf rulers are concerned, there's only one proper way with this and that is: be tough and be tough early."
Manama was effectively shut down. For the first time in the crisis, tanks and armored personnel carriers rolled into the streets and military checkpoints were set up. The Interior Ministry warned Bahrainis in mobile phone text messages to stay off the streets. Banks and other key institutions did not open, and workers stayed home, unable or to afraid to pass through checkpoints to get to their jobs.
Bahrain's parliament - minus opposition lawmakers who are staging a boycott - met in emergency session. One pro-government member, Jamila Salman, broke into tears. A leader of the Shiite opposition Abdul-Jalil Khalil said 18 lawmakers resigned to protest the killings.
Hours after the square was cleared, the military announced a ban on gatherings and said on state TV that it had "key parts" of the capital under its control.
Police prevented people from getting close to the square, which features a 300-foot (90-meter) monument with a giant representation of a pearl atop it, a testament to the island's pearl-diving past.
The smashed tents, broken chairs and other debris that was swept up by authorities was seen dumped in the yard of a police station. Salmaniya hospital was thrown into chaos immediately after the police raid. A steady stream of dozens of wounded from the square were brought in by ambulances and private cars. Nurses rushed in men and women on stretchers, their heads bleeding, arms in casts, faces bruised. At the entrance, women wrapped in black robes embraced each other and wept.
The Health Ministry put the number of wounded at 231.
Many families were separated in the chaos. An Associated Press photographer saw police rounding up lost children and taking them into vehicles.
Britain said it was urgently reviewing arms export licenses to Bahrain. Exports approved in the past nine months include tear gas cartridges and other equipment that can be used for riot control, and the Foreign Office's Middle East and North Africa minister Alistair Burt said it will revoke the licenses if they are judged to be used for facilitating internal repression and human rights abuses.
Elsewhere in the Mideast, several thousand Yemeni protesters defied appeals for calm from the military and the country's most influential Islamic cleric and marched through the capital of Sanaa, clashing with police and government supporters swinging batons and daggers.
Protesters have marched for seven straight days in Sanaa and other cities in Yemen. They demand the resignation of President Ali Abdullah Saleh, a U.S. ally, who has ruled the Arab world's poorest nation for 32 years. The demonstrators' main grievances are poverty and official corruption. Saleh's promises not to run for re-election in 2013 or to set up his son as an heir have failed to quell the anger.
Libyans seeking to oust longtime leader Moammar Gadhafi demonstrated in five cities, defying a crackdown by security forces. Reports emerged that at least 20 demonstrators have been killed in two days of clashes with pro-government groups and security forces. A U.S. rights group said at least 14 people have been arrested. In the capital of Tripoli, government supporters staged counterdemonstrations.
The Bahrain violence forced the cancellation of a lower-tier open-wheel race in Bahrain for Friday and Saturday, and leaves in doubt the March 13 season-opening Formula One race at the same track. Formula One chief Bernie Ecclestone said he will wait until next week to decide whether to proceed with the race. He spoke Thursday to Crown Prince Sheik Salman bin Hamad Al Khalifa about the situation.
Brian Murphy in Dubai, United Arab Emirates, contributed to this report.