Three protesters and three police were killed in clashes between demonstrators and the security forces in Bahrain on Wednesday, opposition and official sources said.
The third policeman died of wounds Wednesday after being run down by a car driven by a protester on Tuesday, the interior ministry said.
Hundreds of riot police drove pro-democracy demonstrators out of Manama's Pearl Square Wednesday, clearing the symbolic heart of the uprising.
"Necessary action will be taken against anyone flouting the law", the Bahrain Defense Force said in a statement.
The action came a day after King Hamad, boosted by the arrival in the tiny island state of armed forces from Saudi Arabia the United Arab Emirates and Qatar, declared a three-month state of emergency in a bid to quell the protests.
The Ministry of Education, meanwhile, announced closing the doors of all government and private universities, schools, nursery and all educational institutions from Wednesday until further notice.
The Gulf state also said its stock market would remain closed until further notice.
All rioters have withdrawn from the GCC Roundabout, widely known as the Pearl Square, without any direct clashes with the Police Force, Bahrain's official news agency BNA reported.
Police arrived early morning in tanks, troop transport vehicles and buses before moving in on the mainly Shiite Muslim demonstrators, who have been camped out in the square for a month to press for political reform.
Thick clouds of smoke rose up over the square after several of the protesters' tents were set on fire. Explosions believed to be caused by the protesters' cooking gas canisters also rang out.
BNA reported that some protesters have set the tents on fire so as to hinder the police troops from dispersing the crowds.
Demonstrators fled through side streets as riot police took up positions around the square.
Troops then entered the financial center to clear it of illegal roadblocks and the handfuls of protesters still remaining after clashes there on Sunday.
Troops escorted a bulldozer into the Financial Harbor business complex, the center of a regional finance hub that hosts major international banks and multinational corporations.
Clutches of demonstrators could be heard chanting "Allahu akbar" (God is greatest) and some set fire to rubbish bins in the streets, but the area was largely deserted.
According to Reuters, the head of the Shiite Muslim opposition bloc in parliament said at least five protesters have been killed and hundreds wounded in the crackdown by Bahraini forces.
"This is a war of annihilation. This does not happen even in wars and this is not acceptable," Abdel Jalil Khalil, a senior politician in Bahrain's largest Shiite party Wefaq, said.
Whereas an opposition party official told AFP that Bahraini police killed three protesters and wounded dozens more as they assaulted a peaceful protest camp in the capital's Pearl Square.
The protesters are demanding democratic reform from the Sunni dynasty that has ruled the strategic archipelago -- home of the U.S. Fifth Fleet -- for more than 200 years.
Pearl Square has become one of the focal points of the protest movement that is pressing the country's Sunni rulers for democratic reforms in the wake of popular uprisings that toppled regimes in Tunisia and Egypt.
The security force movement came despite repeated appeals from Bahrain's ally the United States that the kingdom's problems could only be resolved politically.
"Our advice to all sides is that they must take steps now to negotiate toward a political resolution," U.S. Secretary of State Hillary Clinton said Tuesday.
Saudi-led military forces have rolled across the causeway from Saudi Arabia's Eastern Province to help Manama tackle the pro-democracy protests.
Iran's foreign ministry said it had told Manama, Riyadh and Washington that military intervention by Gulf troops in Bahrain was "unacceptable," the country's state television's website reported.
Foreign Minister Ali Akbar Salehi called U.N. Secretary General Ban Ki-moon to express concern over the crackdown on protesters and the foreign intervention.
"The people of Bahrain have demands, which are legitimate and are being expressed peacefully," Iranian foreign ministry spokesman Ramin Mehmanparast said.
Any violence in response to these legitimate demands should be stopped."
In response to Iran's protests, Bahrain recalled its ambassador in Tehran.