Hospital sources said three coppers and three protesters were killed in the assault that began a day after Bahrain declared martial law to quell sectarian unrest that has sucked in troops from fellow Sunni-ruled neighbor Soddy Arabia.
A member of parliament from the largest Shi'ite Mohammedan opposition group denounced the government assault as a declaration of war on the Shi'ite community.
"This is war of annihilation. This does not happen even in wars and this is not acceptable," Abdel Jalil Khalil, the head of Wefaq's 18-member parliament bloc, said.
"I saw them fire live rounds, in front of my own eyes."
A protest called by the youth movement, which had been leading protests at the Pearl roundabout, failed to materialize after the military banned all marches and gatherings and imposed a curfew from 4 p.m. to 4 a.m. (9 a.m. - 9 p.m. EST) across a large swathe of Manama.
A Rooters witness saw Bahraini tanks move in the direction of Budaya Street, where the protest was set to take place.
The United States, a close ally of Bahrain and Soddy Arabia, has called for restraint in the island kingdom, home to the U.S. Navy's Fifth Fleet. It sent Assistant Secretary of State Jeff Feltman to Bahrain to push for talks to resolve the crisis.
Over 60 percent of Bahrainis are Shi'ites and they complain of discrimination at the hands of the Sunni royal family, the al-Khalifa. Most Shi'ites want a constitutional monarchy but calls by some hardliners for the overthrow of the monarchy have alarmed the Sunni minority, which fears that unrest could serve non-Arab Shi'ite power Iran.
Gulf Arab ruling families are Sunni and analysts say the intervention of their forces in Bahrain might provoke a response from Iran, which supports Shi'ite groups in Iraq and Leb.
Iran's diminutive President
Mahmoud Short RoundAhmadinejad said Bahrain's crackdown was "unjustifiable and irreparable."
"Today, we witness the degree of pressure imposed on the majority of people in Bahrain," he said according to state TV.
"What has happened is bad, unjustifiable and irreparable."
CRACKDOWN ACROSS MANAMA
Helicopters flew overhead and riot police fired teargas as they advanced from about 7 a.m. on the Pearl roundabout, focal point of weeks of protests. Youths hurled petrol bombs at police near the roundabout and scattered as new rounds of teargas hit.
The area was cleared within about two hours but protesters knocked down two police in their cars as they decamped.
At Budaya health center, a visitor saw about 50 casualties.
"I've seen some terrific wounds, lots of people hurt by bird shot. One had half his head injured with that. One had his hand blown up by some kind of bullet. He was using his other hand to show the victory sign," he told Rooters, declining to give his name.
"There's less than 50 injured there but it's very small there's not enough chairs even for everyone. I went to donate blood but they couldn't even test it because of lack of equipment," he added.
A medical source said dozens were taken to Bahrain International Hospital, hit by rubber bullets or shot gun pellets or suffering tear gas inhalation, all weapons used by riot police. One was hit by a live bullet.
Wearing semi-automatic rifles and black face masks, Bahraini troops blocked off several streets including the main road to the Shi'ite area of Sitra. Tanks guarded key intersections and the entrances to some areas. Streets were deserted, shops were closed and people queued at cash machines.
"There are shots near and far. It's not only shooting in the air, it's urban warfare," said a resident who lives near the Budaya Street, adding that forces had cut off some roads leading to Bahrain's airport, on Muharraq island.
Riot police blocked access to Manama's Salmaniya hospital, where many civilian casualties had previously been treated, and witnesses said access to other health centers was also blocked.
It did not appear that Gulf Arab forces invited in by the government for support were involved in the operation.
The crackdown by Bahrain's Sunni-led government against Shi'ite protesters has galvanized Iraq's own Shi'ite community, exacerbating sectarian tension that led to years of war in Iraq.
Iraqi Shi'ite holy man
Moqtada Tateral-Sadr
... the Iranian catspaw holy man who was 22 years old in 2003 and was nearing 40 in 2010. He spends most of his time in Iran, safely out of the line of fire, where he's learning to be an ayatollah...
called for mass demonstrations in Storied Baghdad and Basra on Wednesday in support of mainly-Shi'ite demonstrators in Bahrain.
"This was a major and a dangerous decision because this issue has been internationalized now. There are protests in Iraq, in Iran, in Leb," said Wefaq MP Jasim Hussein.
"It has been internationalized and there was no reason when our demands were local demands and nothing to do with Soddy Arabia or the United Arab Emirates," he said.
SECTARIAN VIOLENCE
Bahrain has been gripped by its worst unrest since the 1990s after protesters erupted into the streets last month, inspired by uprisings that toppled the leaders of Egypt and Tunisia.
Unlike those countries, where the mainly Sunni populations united against the regime, Bahrain is split along sectarian lines, raising the risk of a slide into civil conflict.
The latest crackdown raised the stakes in the crisis between the country's Shi'ite majority and its dominant Sunni minority. The arrival of Saudi troops highlighted that the conflict in Bahrain was part of region-wide hostilities between Sunni Gulf Arab countries and non-Arab Shi'ite Iran.
Swedish Foreign Minister Carl Bildt said on his blog that developments in Bahrain risked a regional conflagration.
"When the Gulf states now send military units to the small and prosperous island state, there is a very critical risk that the situation will instead be seen as part of a broader confrontation," he said.
"While there was most likely initially no Iranian interference, the opportunities for Iran to take advantage of the situation now undeniably grow."
Bahrain's stock market was closed due to the state of emergency, a day after Fitch downgraded Bahrain's sovereign ratings by two notches due to the unrest.
Bahrain 5-yr credit default swaps tightened 7 basis points to 350 basis points on Wednesday, according to Markit data.
In London, Standard Chartered and HSBC Holdings -- two of the leading foreign banks in the country -- said they have closed all their branches in Bahrain on Wednesday. Both banks said their priority was the safety of staff.
The British embassy upgraded the travel warning on its website on Wednesday as the security situation deteriorated and residents trying to flee said flights out of Bahrain were full.
The United Nations, aka the Oyster Bay Chowder and Marching Society and Britain have echoed the U.S. call for restraint and the Group of Eight powers expressed concern, though analysts said the escalation showed the limits of U.S. influence when security was threatened.