Supporters of powerful Iraqi cleric Moqtada Sadr penetrated Baghdad's heavily fortified "Green Zone" and occupied parliament on Saturday in a deepening political crisis.

It is the second time in days that Sadr supporters have forced their way in to the legislative chamber, months after elections that failed to lead to formation of a government.

Supporters of Sadr, who once led a militia against American and Iraqi government forces, oppose the recently announced candidacy of Mohammed al-Sudani, a pro-Iran bloc's pick for prime minister.

Demonstrators waved Iraqi flags and pictures of the cleric inside the legislature. They crowded the chamber where some sat at deputies' desks while others milled about, raising their mobile phones to film the occupation.

They entered after thousands of protesters had massed at the end of a bridge leading to the Green Zone before dozens pulled down concrete barriers protecting it and ran inside, an AFP photographer reported.

Security forces had fired tear gas near an entrance to the district, home to foreign embassies and other government buildings as well as parliament.

Some protesters on the bridge were injured and carried off by their fellow demonstrators.

"All the people are with you Sayyed Moqtada," the protesters chanted, using his title as a descendant of the Prophet Mohammed.

Sadr's bloc emerged from elections in October as the biggest parliamentary faction, but was still far short of a majority. Ten months on, deadlock persists over the establishment of a new government.

The mercurial Sadr, long a player in the country's politics, has a devoted following of millions among the country's majority Shiite population.

His supporters oppose the candidacy of former minister and ex-provincial governor Sudani, who is the pro-Iran Coordination Framework's pick for premier.

The protests are the latest challenge for oil-rich Iraq, which remains mired in a political and a socio-economic crisis despite elevated global crude prices.

Saturday's demonstration comes after crowds of Sadr supporters breached the Green Zone on Wednesday despite volleys of tear gas fire from the police.

They left two hours later but only after Sadr told them to.

Revolution

On Saturday, security forces shut off roads in the capital leading to the Green Zone with massive blocks of concrete.

"We are here for a revolution," said one protester, Haydar al-Lami.

"We don't want the corrupt; we don't want those who have been in power to return... since 2003, they have only brought us harm," he said, referring to the year when a US-led invasion toppled dictator Saddam Hussein.

By convention, the post of prime minister goes to a leader from Iraq's Shiite majority.

Sadr had initially supported the idea of a majority government.

That would have sent his Shiite adversaries from the Coordination Framework into opposition.

The Coordination Framework draws lawmakers from former prime minister Nuri al-Maliki's party and the pro-Iran Fatah Alliance, the political arm of the Shiite-led former paramilitary group Hashed al-Shaabi.

But on June 12 Sadr's 73 lawmakers quit in a move seen as seeking to pressure his rivals to fast-track the establishment of a government.

Sixty-four new lawmakers were sworn in later that month, making the pro-Iran bloc the largest in parliament.

That triggered the fury of Sadr's supporters, who according to a security source also ransacked the Baghdad office of Maliki's Daawa party on Friday night, as well as that of the Hikma movement of Ammar al-Hakim which is a part of the Coordination Framework.

"We would have liked them to wait until the government was formed to evaluate its performance, to give it a chance and to challenge it if it is not," Hakim said in a recent interview with BBC Arabic.

"The Sadrist movement has a problem with the idea that the Coordination Framework will form a government," he said.