Tens of thousands of supporters of an anti-US Shi'ite cleric rallied Thursday at a main downtown square in Baghdad to protest the US military presence and mark the sixth anniversary of the fall of the Iraqi capital to American forces. One of the speakers urged President Barack Obama, who made a brief visit to Baghdad this week, to remove all US troops "to fulfill the promises he made to the world." Cleric Muqtada al-Sadr had urged all Iraqis to turn out for the protest at Firdous Square - where Saddam Hussein's statue was toppled on April 9, 2003. The crowd burned an effigy of Obama's predecessor George W. Bush as it hung from the pillar where Saddam's statue once stood. "We demand that President Obama stand with the Iraqi people by ending the occupation to fulfill his promises he made to the world," al-Sadr aide Assad al-Nassiri told the crowd. The aide read out comments by al-Sadr, who lives in Iran, in which he described the US presence as a "crime against all Iraqis" and demanded the release of all detainees. Security was tight with police blocking off streets leading to the square, mindful of the threat of car bombs which have struck the city in recent days. Al-Sadr had called for a "march of the millions" but it appeared the crowd numbered no more than 30,000 before protesters dispersed late in the morning. Protesters waved Iraqi banners and carried pictures of al-Sadr, chanting: "No, no occupation" and "Long live al-Sadr!" Huge Iraqi flags decorating the square hung drenched from the heavy rain that had pelted the city Thursday morning. Iraqi police guarded the rally but kept away from the main square. Armored Iraqi and American vehicles were parked a few blocks away. One of the protesters, Ammar Mahdi, 23, said he walked five miles to join the rally to demand the "immediate withdrawal of the US soldiers who brought destruction to Iraq instead of freedom." Obama has pledged to remove all combat troops by September 2010 and the rest of the US force by the end of 2011. Despite the anti-US comments, the tone of the speeches seemed less hostile than before Obama's election, when Sadrists would avoid referring to Bush as president. Salah al-Obeidi, spokesman for the movement, said the change in tone was intentional and an overture to the new US administration. "We see some change in Obama's language," he said. "It seems to us that Obama does not want to use Iraq as a base to fight al-Qaida." The protest against the US presence contrasted with the jubilation of six years ago, when crowds of Iraqis cheered as American Marines hauled down Saddam's statue marking the collapse of his regime. But the years of violence, bloodshed and political turmoil that followed soured many Iraqis on the US role, even though there is public unease over the capability of Iraqi forces to maintain security once the Americans have gone. "I am among those who were glad when the former regime fell. We chanted and cheered," said Baghdad schoolteacher Hashim Mohsen. "We thought new loyal people were leading the country into a new prosperous era. But regrettably, there is not what occurred." The demonstration coincides with an uptick in bombings of Shi'ite targets around the city, undermining public confidence in Iraq's army and police. At least 53 people have been killed in bombings in Shi'ite areas of Baghdad this week. The government has blamed Saddam supporters in league with al-Qaida for the blasts.