Anti-US Shia cleric Moqtada Sadr has told an enthusiastic crowd of followers in Iraq to give the country's new government a chance.
The radical cleric was making his first speech since returning to his stronghold in Najaf after nearly four years of self-imposed exile in Iran.
Last month his movement secured a deal to join the new government with seven ministries and 39 seats in parliament.
He urged resistance against "occupiers of Iraq" and led chants against the US.
His militia, the Mehdi Army, clashed several times with US and Iraqi forces after the 2003 US-led invasion.
At the start of his short speech, the cleric called on the crowd of thousands to chant "No, no, to America", rejecting all occupiers and denouncing Israel.
"We are still fighters," he told the crowd. "We are still resisting, we resist the occupation, militarily, culturally and all other kinds of resistance."
But he included the caveat that arms were for "people of weapons only" - seemingly endorsing the authority of Iraq's army and police force.
The cleric exhorted Iraqis to forget what happened in the past and stand shoulder to shoulder, helping the government to provide services.
"The Iraqi government has been formed," he said. "If it serves the Iraqi people, and provides services, we will stand by it, not against it.
"All of us will be with the Iraqi government if it serves the Iraqi people. If it doesn't, there are political - only political - ways to reform the government.
"This is a new government, we must give it a chance to prove that it can serve the people," he added, in what analysts suggest was a more statesmanlike performance than had been seen previously.
Sunnis will be reassured by that message, says the BBC's Jim Muir in Baghdad, but they will want to see it turned into reality.
Having arrived back in the country on Wednesday, on Thursday the cleric visited one of the holiest sites of Shia Islam, the shrine of the Imam Ali.
Thousands of his supporters gathered at the site, chanting loudly and causing a stampede as they jostled to see him.
He later issued a statement criticising their behaviour, begging his supporters "to be disciplined, and not to shout excessive slogans".
Our correspondent says that despite his near four-year absence, the charismatic Moqtada Sadr has lost none of his influence on the largely impoverished Shia population of Iraq.
But the situation in Iraq has changed since the cleric fled the country after a warrant was issued for his arrest.
His militia was blamed for the abduction, torture and killing of thousands of Sunnis during the sectarian carnage of 2006 and 2007.
In 2008, the militia clashed with the Iraqi army, commanded by Prime Minister Nouri Maliki, and many members were arrested; Moqtada Sadr announced it was laying down arms and disbanding.
But the cleric's support was vital in securing Mr Maliki's second term in office, and his movement is now closely involved in the new government.
With the US preparing to withdraw all its forces in 2011, the emphasis in Iraq is now on supporting the government and promoting unity and prosperity, says our correspondent.