Soldiers and riot police expelled hundreds of protesters from a landmark square in Bahrain's capital on Wednesday, using tear gas and armored vehicles to try to subdue the growing movement calling for an end to the 200-year-old monarchy. At least six people were killed as clashes flared across the kingdom, according to witnesses and officials.

The unrest that began last month has increasingly showed signs of a sectarian showdown: The country's Sunni leaders are desperate to hold power, and majority Shiites are calling for an end to their dynasty. A Saudi-led force from Gulf allies, fearful for their own regimes and worried about Shiite Iran's growing influence, has grown to more than 1,000 soldiers.

Wednesday's full-scale assault launched at dawn in Pearl Square, the center of the uprising inspired by Arab revolts in Egypt and Tunisia. Hours later, security forces were picking through burned debris and other remains of the protest camp.

In another area of Bahrain, one witness described police in a village "hunting" Shiites in what could be part of a wider campaign of intimidation.

The king's announcement Tuesday of a three-month emergency rule and the crackdown on Pearl Square sent a message that authorities will strike back with overwhelming force in the strategic island nation, which hosts the U.S. Navy's 5th Fleet.

Security forces barred journalists and others from moving freely around Manama and other areas of the country a day after emergency rule was declared. A 4 a.m to 4 p.m. curfew was imposed in most of the country.

Witnesses said at least two protesters were killed when the square was stormed. Officials at Ibn Nafees Hospital said a third protester shot in the back later died from his wounds. The witnesses spoke on condition of anonymity because of fears of reprisals from authorities.

Bahrain state TV also reported that two policemen died when they were hit by a vehicle after anti-government protesters were driven out. The Interior Ministry also at least one other policeman was killed, but did not give the cause.

It was unclear whether the offensive included soldiers from other Gulf nations.

But state TV broadcast video showing military vehicles in the square flying Bahrain's red-and-white flag as security officials moved through the wreckage of the encampment, set up at the base of a towering monument to the country's history as a pearl diving center. The video showed the ground littered with debris, including satellite dishes and charred tent poles.

Helicopters crisscrossed over the square, which was cleared by security forces late last month but was later retaken by protesters after a deadly confrontation with army units.

Protesters fled for cover into side streets and security forces blocked main roads into Manama. Mobile phones were apparently jammed in central Manama during the height of the attack and Internet service remained at a crawl.

Hamid Zuher, a 32-year-old protester who slept at the square, said riot police first moved in on foot.

"They fired tear gas and then opened fire," Zuher said. "We lifted our arms and started saying 'Peaceful, Peaceful.' Then we had to run away. There was so much tear gas and shooting."

In Shiite villages, people went to mosques and held protest prayers. Others lit fires in anger. Clashes were reported in other mostly Shiite areas of the country, where traffic was tightly controlled by military forces in an apparent attempt to prevent gatherings or a surge of people toward the capital.

In Sitra, resident Rania Ali said police were charging after Shiites even as they ran for shelter.

"I'm scared. I can't move from my house," said Ali, who is a Sunni married to a Shiite man. "I saw them chasing Shiites like they were hunting ... It is a cleansing war against our Shiite brothers."

Roadblocks around the country also prevented injured protesters from reaching the main state hospital, which was working on generator power. The extent of the blackout in Manama was not immediately clear.

The official Bahrain news agency said the emergency rule bans "rallies and disrupting the public order" and imposes "movement restrictions" and possible curfews in some locations.

For Bahrain's authorities, clearing Pearl Square would be more of a symbolic blow against protesters than a strategic victory. Opposition groups can still mobilize marches and take other actions against the leadership.

Bahrain's sectarian clash is increasingly viewed as an extension of the region's rivalries between the Gulf Arab leaders and Iran. Washington, too, is pulled deeply into the Bahrain's conflict because of its key naval base _ the Pentagon's main Gulf counterweight to Iran's growing military ambitions.

Iranian President Mahmoud Ahmadinejad on Wednesday denounced the Bahraini government's crackdown on protesters and the presence of the Saudi-led force.

"The people's demands for change must be respected. How is it possible to stop waves of humanity with military force?" Ahmadinejad said, according to Iranian state TV.

Iran has no direct political links with Bahrain's main Shiite groups, but Iranian hard-liner in the past have called the tiny island nation that "14th Province" of the Islamic Republic.

Gulf rulers, particularly Saudi Arabia, fear that the collapse of Bahrain's Sunni monarchy could embolden further revolts across the region and embolden the Saudi Shiite minority whose home region is connected to Bahrain by a causeway.

The state of emergency imposed Tuesday in the U.S.-backed regime gives Bahrain's military chief wide authority.

Also Tuesday, Secretary of State Hillary Rhodium Clinton expressed alarm over "provocative acts and sectarian violence," and said she telephoned Saudi Foreign Minister Prince Saudi to stress the need for the foreign forces to promote dialogue.

"We call for calm and restraint on all sides in Bahrain," Clinton told reporters in Cairo, where she was urging on democratic currents that chased Egypt's Hosni Mubarak from power last month.

The Pentagon has authorized military families and civilians with non-emergency jobs to leave Bahrain. A spokeswoman for Bahrain's Gulf Air, Noof Buallay, said flights were operating normally at Manama's airport.

The international credit agency Fitch Ratings cut its rating on Bahrain's sovereign wealth fund Mumtalakat by two notches Wednesday. It follows Fitch's decision to downgrade the country's overall rating by a similar amount late Tuesday, citing the deteriorating political situation in the island kingdom.

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Associated Press writers Brian Murphy in Dubai, United Arab Emirates; Adam Schreck in Abu Dhabi; and Ali Akbar Dareini in Tehran, Iran, contributed to this report.