BAGHDAD — Six years after the U.S. overthrew Saddam Hussein's government, tens of thousands of Iraqis gathered in the rain in Iraq's capital Thursday to mark the anniversary and renew calls for an American withdrawal.

The demonstrators came in response to calls by Muqtada al Sadr, the influential Shiite cleric who's long decried the U.S. military's occupation, but there were also Sunni Muslims in the crowd.

Draped in Iraqi flags and chanting, protesters packed Baghdad's Firdous Square, where six years ago a crowd cheered the destruction of a statue of Saddam.

"No, no to America," demonstrators repeated Thursday. "No, no to arrogance."

Speakers at the rally called on President Barack Obama to "keep his promise to the world" and withdraw U.S. troops quickly.

"I hope that all the sons of the fervent Iraqi people in all their shades — Sunni and Shiite, Arab and Kurd, Christian, Sabian and Muslim — will participate in this demonstration to reject the despicable occupation," Sadr said in a statement announcing the event two weeks ago.

Obama, who this week made his first visit to Iraq since he became president, has pledged to pull most American troops from Iraq by next summer. In Baghdad on Tuesday, he said that a recent uptick in violence in Iraq hadn't changed those plans.

Besides an end to the occupation, rally speakers called for "Iraqi unity."

Police said that many Sunnis, including prominent leaders, took part.

Among the Sunni leaders was Hameed al Hayis, who helped launch the Sons of Iraq, groups of Sunni militiamen whom the U.S. began paying in 2007 to ally with Americans and help root out al Qaeda in Iraq. Many Sons of Iraq members are former insurgents.

More recently, Hayis formed a majority-Sunni political party that's openly critical of Iraq's Shiite-led government, and won two seats on Anbar's provincial council in January.

In a speech Thursday, Hayis demanded that the government release Shiite Sadrist prisoners and that high-ranking government security officials resign. The recent spike in violence proves that they're unqualified, he said.

His attendance Thursday suggests that his party may be looking to strike an alliance with Sadrists, a possibility that Hayis didn't rule out in an interview after the demonstration.

"Our Sadrist brothers have a clear vision. We appreciate that they don't compromise on that," he said. "They don't want an occupation on their land."

Any alliance shouldn't come as a surprise, Hayis added: "This is only an unusual idea to people with short memories, because we must remember there was a time when we were all Iraqis. The divisions only came when the Americans came."

For years after the U.S.-led invasion, Sadr's Mahdi Army militia battled American troops. Seen at first as a national resistance force against the occupation, his militia later became feared by Sunnis as sectarian violence spread.

Last year, Sadr ordered the Mahdi Army to lay down its weapons and turn its focus to social and cultural causes, one of several factors that led to last year's drop in violence. Sadr now lives in Iran, where he's studying Islam.

Demonstrators also gathered Thursday in Fallujah, though in far smaller numbers than in Baghdad.

"I would like to register for history that America should be held accountable for the terrorism in our country," said one demonstrator, Kathemiyah Jawad. "The Americans said they want to spread democracy and freedom, but we have seen neither."

Another protester, Abu Hammad, said he'd come out to march every time Sadr had asked. "Anyone would reject a situation of occupation upon his land and people," he said. "And if the occupation continues, we will chant, 'Yes, yes to martyrdom.' "

(Reilly reports for the Merced (Calif.) Sun-Star. Issa is a McClatchy special correspondent.)

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