(CNN) -- Shiite cleric Muqtada al-Sadr, the anti-American political figure who returned to Iraq this week from self-imposed exile, told tens of thousands of his followers Saturday to "resist" and "disturb" the United States.
"We have not forgotten the occupier. We remain a resistance," said al-Sadr, delivering a fiery speech in the holy Shiite city of Najaf, his first public address in Iraq in years. "We continue to resist the occupier militarily, culturally and by all means of the resistance."
Al-Sadr, who spent more than three years in self-imposed exile in the predominantly Shiite Iran, took to the podium amid tight security.
As he exhorted Iraqis to unite and end the infighting that has plagued the ethnically and religiously mixed country, the crowd chanted "No, no to America" and "No, no to the occupier," waved Iraqi flags, and carried the portraits of al-Sadr and other Shiite figures.
"Whatever struggle happened between brothers, let us forget about it and turn the page forever and live united," al-Sadr said. "We do not kill an Iraqi."
He noted that politics in recent days has dominated Iraq, which recently formed a government after months of political feuding that followed the March 7 elections. Amid this activity, he said, "it made us forget the resistance and the occupier leaving."
But he reminded the crowd that "our main goal as Iraqi people is to drive the occupation out in any way," but he said resistance doesn't "mean everyone carry arms."
"We also resist through cultural resistance. Our rejection of the occupier at heart is resistance."
The less than 50,000 U.S. troops remaining in Iraq are slated to leave the country at the end of the year under a bilateral security agreement, and Prime Minister Nuri al-Maliki is emphasizing that there will be no extension of U.S. forces after December 31.
Al-Sadr made an apparent reference to this, saying "we heard a pledge from the Iraqi government that it will get the occupier out and we are waiting for it to fulfill its pledges."
As for the new Iraqi government, al-Sadr said that if it provides "security, safety and services, then we are with this government not against it."
"If it does not serve the Iraqi people, there are only political means that must be followed to reform the government -- a new government that we must give a chance to prove that it is there to serve the people," he said.
Al-Sadr left Iraq as the leader of the Mehdi Army, the notorious Shiite militia that fought some of the fiercest battles against U.S. forces in 2004 and 2008. He returned from neighboring Iran as the head of a political force in Iraq more organized than ever.
Observers believe al-Sadr is working to transform his group into a sophisticated and populist political movement, a development that belies that group's militant activity and rhetoric over the years.
His political bloc, which won 39 seats in last year's parliamentary elections, emerged as a kingmaker in Iraqi politics, ending months of political deadlock after throwing its support behind al-Maliki and helping to guarantee his second term.
Analysts believe Iranian influence was behind the deal and Sadrist political muscle is behind al-Maliki's stated opposition to keeping U.S. troops after next year.
Al-Sadr's politicians have at least seven ministries in the newly formed government in addition to the key post of one of the two deputy speakers of parliament.
Since 2003, al-Sadr has had the support of tens of thousands of Shiites, especially the young and impoverished in Baghdad's slums and the Shiite south. His return Wednesday raised some concerns that it could stoke sectarian divides.
The Mehdi Army was blamed for some of the worst sectarian violence in Iraq before al-Sadr suspended most of its activities in 2007 and 2008.
While the Mehdi Army has been largely underground for more than two years, there have been fears that they have not given up arms and can potentially destabilize the country, with some of its forces still active in targeting U.S. forces.
In 2008, Sadr announced that most of the militia members would be transitioned into a socio-cultural organization to oppose secularism and Western thought.
A small group of hand-picked fighters called the Promised Day Brigade would continue to target the coalition, the U.S. military has said.
His speech Saturday came as no surprise to the United States.
"We listened to the speech, but heard nothing new," U.S. Embassy spokesman David J. Ranz told CNN.
While American officials have publicly welcomed al-Sadr's active participation in the government they also have voiced concern about them resorting to violence.
"Our concerns with the Sadrists is not so much their political philosophy; there are many political groups with political philosophies of many different flavors. Our concern with them is the fact that we do not see compelling evidence that they have renounced in practice and in theory the idea that they can use armed force against their opponents," U.S. Ambassador to Iraq James Jeffrey told reporters in a recent briefing.