Anti-US Shia cleric Moqtada Sadr has received an enthusiastic welcome in the Iraqi city of Najaf.
Following chaotic scenes as he visited a shrine, Moqtada Sadr urged his supporters to show discipline.
The radical cleric has returned to his stronghold in the city after three years in self-imposed exile in Iran.
The militia founded by Moqtada Sadr, the Mehdi Army, clashed several times with US and Iraqi forces after the 2003 US-led invasion.
But last month, his political movement secured a deal to be part of the new government, with 39 parliamentary seats and seven ministries.
Moqtada Sadr arrived back in Iraq on Wednesday after more than three years in Iran.
On Thursday he visited one of the holiest sites of Shia Islam, the shrine of the Imam Ali, where thousands of his supporters gathered, chanting loudly and causing a stampede as they jostled to see him.
"His return is a victory for just people. It's a great pleasure for us, especially because his movement is to participate in the government," one Sadr supporter told AFP news agency.
"That means there that no security problems will happen - no battles or confrontation with the government, as happened before."
Moqtada Sadr later issued a statement criticising his followers' behaviour, telling them: "I did not know you like that."
"Your indiscipline while I was performing my religious rituals bothered me and hurt me. I beg you to be disciplined, and not to shout excessive slogans," he said.
"The stampede hurt me, and hurt others, and this will tarnish the image of our movement in the eyes of others."
The BBC's Jim Muir in Baghdad says that despite his 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, our correspondent adds.
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.