Updated

Anti-American Shiite cleric Muqtada al-Sadr urged Iraq's parliament to reject a pact that would extend U.S. presence in Iraq for three years as tens of thousands of his followers marched through Baghdad's streets Saturday to reinforce that demand.

The large turnout points to trouble ahead for the U.S.-Iraqi security deal as Sunni and Shiite lawmakers weigh the political risks associated with the far-reaching agreement.

Waving Iraqi flags and green Shiite banners, protesters chanted slogans condemning the pact. The demonstration in the mostly Shiite eastern part of Baghdad was staged under tight security, with army soldiers and police manning checkpoints along the route.

"I am with every Sunni, Shiite or Christian who is opposed to the agreement ... and I reject, condemn and renounce the presence of occupying forces and bases on our beloved land," al-Sadr said in a message read to the crowd on his behalf by a senior aide.

The pact, reached after months of bitter negotiations, governs the presence in Iraq of U.S. troops after their U.N. mandate expires Dec. 31. As copies of the draft became available this week, it sparked an intensely public debate among top politicians.

A copy of the draft accord obtained by The Associated Press specifies U.S. troops must leave Iraqi cities by the end of June and be gone by 2012. It gives Iraq limited authority over off-duty, off-base U.S. soldiers who commit crimes. U.S. Congressional approval is not required for the pact to take effect, but the Bush administration is trying to build maximum political support anyway.

But in Iraq, the pact must be ratified by the 275-seat parliament — riven by the narrow partisan interests, sectarian and ethnic divisions that have defined Iraqi politics since the 2003 ouster of Saddam Hussein.

Next year's provincial and national elections further complicate the pact's approval.

Positions taken on the security pact could determine how political parties fare at the ballot box, with most voters anxious to see U.S. troops leave and Iraq become a truly sovereign nation again.

"It is not going to be easy to have parliament adopt the agreement," said senior Kurdish politician and lawmaker Mahmoud Othman, warning approval will likely be a drawn out process.

That has left everyone hedging his position on the agreement — except for al-Sadr, who lives in Iran but controls 30 seats in parliament.

"I am confident that you brothers in parliament will champion the will of the people over that of the occupier ... Do not betray the people," al-Sadr said in his message, as the crowd chanted "Occupier, get out," and "No, no to America. No, no to the agreement."

The turnout was expected since al-Sadr's ability to bring out supporters was never in doubt, but it crushed any hope the Sadrist bloc would support the agreement or remain neutral.

Al-Maliki, a Shiite, faces political isolation trying to win parliament's backing in the face of widespread opposition.

So far, the prime minister has said little in public to suggest wholehearted support of the pact. In comments aired on state television Friday, he said the draft contained "positives, weaknesses, and negatives."

His aides say he told the country's senior politicians this week, the draft agreement was the best his negotiators could get.

Foreign Minister Hoshyar Zebari told reporters Saturday he thought it would be "difficult to reopen negotiations," but sought to counter criticism of the agreement, saying it was temporary and subject to an annual review.

The key to approval of the pact is the Supreme Islamic Iraqi Council, the largest Shiite party and al-Maliki's senior coalition partner. The Supreme Council maintains close ties with Iran but has also been a reliable partner of the United States in Iraq.

"It is a tough issue because the public has been kept in the dark about it," said Jalaluddin al-Saghir, a senior council lawmaker who attended al-Maliki's meeting with political leaders. "We don't yet have a final position on its contents."

But Othman said the Supreme Council's reluctance to sign off on the agreement may have something to do with its Iranian ties.

"They must consider Iran as they deal with this," Othman said, alluding to Tehran's opposition to the deal.

The 54-seat Kurdish bloc in parliament supports the agreement. But the largest Sunni Arab bloc — the 44-seat National Accordance Front — has been hesitant to take a public position.

Front spokesman Salim Abdullah said the group was studying the document, but added that it has placed many politicians in an "awkward" position.

"The Iraqi and Arab streets perceive the agreement as biased in favor of the Americans. So how can political forces here take a balanced position?" he told The Associated Press. "I find many of its articles to be good and beneficial for Iraq and that the American administration made some big concessions. But it's difficult to market it."