Shiite cleric Moqtada al-Sadr, who returned to Iraq after four years of exile in Iran, urged his followers Thursday to remain calm after they gave him a rowdy welcome in his home city Najaf.

Hundreds of people turned out to greet the radical cleric when he arrived on Wednesday in the central Iraq city but apparently became too exuberant when he later visited the shrine of Imam Ali and caused a stampede.

"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," Sadr said in a statement.

"The stampede hurt me, and hurt others, and this will tarnish the image of our movement in the eyes of others," the cleric said.

Sadr, who according to a source in his movement left Iraq at the end of 2006, has so far remained mum about the reasons for his return from his self-imposed exile.

The son of revered Grand Ayatollah Mohammed Sadiq al-Sadr, he had reportedly been pursuing religious studies in the Iranian holy city of Qom.

The cleric, who is said to be in his 30s, gained wide popularity among Shiites in Iraq in the months after the US-led invasion of 2003, and in 2004 his Mahdi Army militia battled US troops in two bloody conflicts.

He was identified by the Pentagon in 2006 as the biggest threat to stability in Iraq.

His militia became the most active and feared armed Shiite group, and was blamed by Washington for death-squad killings of thousands of Sunnis.

But in August 2008, Sadr suspended the activities of his Mahdi Army, which once numbered in the tens of thousands, following major US and Iraqi assaults on its strongholds in Baghdad and southern Iraq in the spring.

Following the ceasefire, US military commanders said his action had been instrumental in helping bring about a significant decrease in the levels of violence across Iraq.