Bahrain armed forces clamped down on the fourth day of demonstrations in Manama early Thursday morning, effectively shutting down the capital.
Riot police stormed Pearl Square in the pre-dawn hours while most of the protesters were asleep in their tents, firing tear gas and rubber bullets as demonstrators scrambled out of their tents and fled the area.
Early reports indicate that at least four demonstrators were killed.
Armed police units patrolled the neighborhoods, blocking access to the square from surrounding streets with barbed wire barriers.
For the first time since the demonstrations began, tanks and armored personnel carriers positioned themselves around the square, which the government declared off limits.
The Interior Ministry used text messages to warn people to stay inside and off the streets.
"The Ministry of the Interior warns all citizens and residents not to leave the house due to potential conflict in all areas of Bahrain," the message read.
Clashes between police and rock-throwing demonstrators continued at various locations throughout the morning hours.
One eyewitness said riot police surrounded the square early to take advantage of the absence of media.
"They moved in as soon as the media left us. They knew what they were doing," The Associated Press quoted Mahmoud Mansouri saying.
"We yelled, 'We are peaceful! Peaceful!'" he said. "The women and children were attacked just like the rest of us."
"They attacked our tents, beating us with batons," a 17-year-old said. "The police were lined up at the bridge overhead. They were shooting tear gas from the bridge."
"Then, all of a sudden, the square was filled with tear gas clouds. Our women were screaming," another protester said. "What kind of ruler does this to his people? There were women and children with us."
The uprising in Bahrain pits the ruling Sunni monarch against the protest movement composed mainly of Shiite Muslims. On Wednesday evening, a Shiite imam told protesters not to back down.
"This square is a trust in your hands and so will you whittle away this trust or keep fast?" he asked them. "So be careful and be concerned for your country and remember that the regime will try to rip this country from your hand, but if we must leave it in coffins, then so be it!" he said.
Meanwhile in Libya, government forces killed at least 14 protesters in four cities on Wednesday, as protesters carried banners reading "Down with Gadhafi. Down with the Regime."
"Internal security forces and militias of the Revolutionary Committees used live ammunition to disperse a peaceful demonstration by the youth of al-Baida," the London-based Libya Watch reported.
The Geneva-based Human Rights Solidarity quoted eyewitness testimonies that claimed snipers positioned on rooftops had shot dead more than 10 protesters and wounded dozens.
Videos posted on the Internet showed young Libyans in the city chanting "The people want to bring down the regime," as flames shot from a building behind them.
Protesters kicked off a countrywide "Day of Rage" on Thursday, as the youth posted text messages warning the government not to cross their "four red lines," namely Moammar Ghadafi, territorial integrity, internal security and Islam."
"We will confront anyone in any square or avenue of our beloved country," the youth wrote, while Ghadafi's regime warned they would not tolerate anyone who tried to "plunder the achievements of the people and threaten the safety of citizens and the country's stability."
AP contributed to this report.