Bahraini police on Sunday clashed with demonstrators trying to occupy Manama's banking center, as protests spread from a peaceful sit-in to the heart of the strategic Gulf state's business district.
Witnesses said police fired tear gas and rubber bullets at around 350 activists who had sealed off the Financial Harbour business complex with road blocks and a human chain.
Thousands of protesters, however, returned to the area later in the afternoon, residents said.
A video uploaded on Sunday to YouTube purports to show Bahraini riot police shooting an unarmed protester in the head at point-blank range with a tear gas round.
The man appears to be remonstrating with helmeted riot police when they shoot him twice from just meters (yards) away -- once in the body and, when he tries to get up, a second time in the face.
The user who posted the 33-second clip claims it was filmed during Sunday's unrest in Manama, but the authenticity of the video could not immediately be verified.
Hospital sources said around 200 people had been hurt in the violence, mainly from inhaling tear gas. They said three were in critical condition, including one with severe head injuries.
The interior ministry said 14 policemen were injured.
Meanwhile, regime loyalists armed with knives and clubs fought students at the university.
"The regime is using thugs," said Khalil Marzooq, a member of the main Shiite opposition group.
Police also fired tear gas at protesters occupying Pearl Square, the epicenter of the protests, which is a short distance from the financial district, witnesses said.
Bahrain -- home of the U.S. Fifth Fleet -- has become a regional financial hub as it seeks to diversify its economy away from a dependence on diminishing oil revenues.
Bahrain's crown prince renewed his call for national dialogue on Sunday, promising the talks would address key demands such as bolstering the power of parliament and that any deal could be put to a referendum.
In a statement read on Bahrain TV, Sheikh Salman al-Khalifa said talks would also cover electoral and governmental reforms, as well as looking into claims of corruption and sectarianism.
"We have worked actively to establish contacts to learn the views of various sides... which shows our commitment to a comprehensive and inclusive national dialogue," the statement said.
The main opposition groups have stopped short of demanding the toppling of the king, but more extreme hardliners have been vocal in calling for the end of monarchy.
Gates said he told Bahrain's leaders -- who have promised to create jobs and provide more cheap housing in response to the protests -- to quickly adopt far-reaching reforms or risk being swamped by the tide of democratic change sweeping the Arab world.
"I told both the king and the crown prince that across the region I did not believe there could be a return to the status quo ante," he told reporters after the talks.
Meanwhile, Bahrain's main trade union announced an open-ended strike from Sunday in protest at the use of force against demonstrators.
"This is in violation of human rights and international conventions ratified by the kingdom of Bahrain," said the General Federation of Workers Trade Unions.
The Iranian-backed Shiite Lebanese movement Hezbollah condemned "the excessive use of violence to suppress peaceful demonstrations by the people of Bahrain who are seeking to secure their legitimate political rights."