Bahraini forces, backed by helicopters are firing tear gas in a crackdown on protesters.

The troops are clearing hundreds of protesters from a camp that had become the symbol of an uprising by the island’s Shi’ite Muslim majority.

Three policemen and two protesters have reportedly been killed in the assault, which began a day after Bahrain declared martial law to quell worsening sectarian unrest.

Fellow Sunni-ruled neighbour Saudi Arabia, has sent 1000 soldiers to Bahrain and the United Arab Emirates has provided the kingdom with 500 police. Iran has condemned the assistance.

Helicopters flew overhead and riot police fired teargas as they advanced from about 7am 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 fled.

Wearing semi-automatic rifles and black face masks, Bahraini troops also blocked off several streets including the main road to the Shi’ite area of Sitra. 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 Highway in the northwest of Bahrain, adding that forces had cut off three bridges linking Bahrain’s airport, on Muharraq island, to the main 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 centres was also blocked.

A defiant youth movement, which had been leading the Bahraini protests, called for a mass demonstration from all suburbs in Manama, the capital, towards Budaya Street in the north of the city.

Earlier a Bahraini defence official warned Bahrainis not to gather in public, saying it was for public safety.

A member of parliament from the largest Shi’ite Muslim 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.”

He said at least five people had been killed by security forces who fanned out across the Manama. There was no independent confirmation.

The United States, a close ally of Bahrain and Saudi Arabia, has called for restraint in the island kingdom, home to the US Navy’s Fifth Fleet. It sent U.S. Assistant Secretary of State Jeff Feltman to Bahrain to push for talks to resolve the crisis.

More than 60 percent of Bahrainis are Shi’ites who complain of discrimination at the hands of the Sunni al-Khalifa royal family.