Tens of thousands draped themselves in Iraqi flags and marched through the streets of two Shiite holy cities Monday to mark the fourth anniversary of Baghdad's fall. The rally was called for by powerful Shiite cleric Muqtada al-Sadr, who commands an enormous following among Iraq's majority Shiites and has close allies in the Shiite-dominated government. A day earlier, the renegade cleric issued a statement ordering his militiamen to redouble their battle to oust American forces and argued that Iraq's army and police should join him in defeating "your archenemy." On Monday, thousands of demonstrators marched from Kufa to neighboring Najaf, 160 kilometers (100 miles) south of Baghdad, with two cordons of Iraqi police lining the route. Some at the rally waved small Iraqi flags; others hoisted up a giant flag 10 meters (yards) long and carried it overhead. Flashing victory signs, they chanted "We obey your call!" and some echoed al-Sadr's statement from a day earlier. "The enemy that is occupying our country is now targeting the dignity of the Iraqi people," said lawmaker Nassar al-Rubaie, head of Sadr's bloc in parliament, as he marched. "After four years of occupation, we have hundreds of thousands of people dead and wounded," he said. Leaflets fluttered through the breeze reading: "Yes, Yes to Iraq" and "Yes, Yes to Muqtada. Occupiers should leave Iraq." Iraqi soldiers in uniform joined the crowd, which was led by at least a dozen turbaned clerics - including one Sunni. Many marchers danced as they moved through the streets. The demonstration was peaceful, but two ambulances could be seen moving slowly with the marching crowd, poised to help if violence or stampedes broke out. Cars were banned from Najaf for 24 hours starting from 8 p.m. Sunday, said police spokesman Col. Ali Jiryo. Buses idled at all entrances of the city to transport arriving demonstrators or other visitors to the city center. Najaf residents would be allowed to drive, he said. Security was tight across Iraq, with a 24-hour ban on all vehicles in Baghdad starting from 5 a.m. Monday. The government quickly reinstated Monday as a holiday, just a day after it had decreed that April 9 no longer would be a day off. Monday's demonstration marks four years since US Marines and the Army's 3rd Infantry Division swept into the Iraqi capital 20 days into the American invasion. In a statement distributed in Najaf on Sunday, al-Sadr called on Iraqi forces to stop cooperating with America. "You, the Iraqi army and police forces, don't walk alongside the occupiers, because they are your archenemy," the statement said. He urged his followers not to attack fellow Iraqis but to turn all their efforts on American forces. "God has ordered you to be patient in front of your enemy, and unify your efforts against them - not against the sons of Iraq," it said. Al-Sadr had reportedly ordered his militia to disarm and stay off the streets during a Baghdad security crackdown that began Feb. 14, though he has nevertheless issued a series of sharp anti-American statements, demanding the immediate withdrawal of US troops. US officials have said al-Sadr left Iraq for neighboring Iran after the start of the crackdown, but his followers say he is in Iraq. Sunday's statement was apparently issued in response to three days of clashes between his Mahdi Army militiamen and US-backed Iraqi troops in Diwaniyah, south of Baghdad. American troops continued operations in Diwaniyah on Monday, detaining four guards at the office of a Shiite political party and scouring two neighborhoods in the city's northern and eastern sections, police said. At least 24 suspects were detained, police said. US officials had no immediate comment. Diwaniyah lies 130 kilometers (80 miles) south of Baghdad On Sunday, thousands of residents in Baghdad's largest Shiite slum, Sadr City, boarded buses and minivans bound for Najaf. Iraqi flags flew from most houses and shops in Sadr City. Drivers and motorcyclists affixed them to their vehicles. Police escorted convoys of pickup trucks overflowing with young boys waving Iraqi flags, en route to Najaf. Despite the curfews, violence persisted Monday. In southern Baghdad, a sniper killed a civilian and a policeman and a mortar round killed one person and wounded two others, police said. Gunmen ambushed a doctor on his way to work in Hilla, about 95 kilometers (60 miles) south of Baghdad, police said. The man's fate was unknown.