Radical Shiite cleric Moqtada al-Sadr returned to Iraq today for a hero's welcome in his stronghold of Najaf after nearly four years outside the country, an AFP correspondent said.

"Moqtada al-Sadr has returned to his home in Najaf. He arrived about 3:00 pm (1200 GMT) with several leaders from the Sadr movement," a source in his movement said, adding Sadr was not visiting but had returned to stay.

Hundreds of supporters took to the streets of Al-Hanana neighbourhood in Najaf, the central Iraq shrine city where Sadr's home is located, to celebrate the cleric's return watched on by security forces.

"I cannot express my happiness when I heard the news of Moqtada's arrival," said Mohamed Hussein, 33, a Najaf resident. "I came running to be sure that Sayyid Moqtada is in Najaf."

"I couldn't believe that Sadr is in Najaf," said Ahmed Kadhim, 44, also a resident of the city. "I came to Al-Hanana to be sure of the news."

Sadr, who wore the black turban of a "sayyid," or descendant of the Prophet Mohammed, visited the shrine of Imam Ali, one of the most revered sites in Shiite Islam, about 5:00 pm (1400 GMT), with a group of grey-clad bodyguards in tow.

He is to meet Grand Ayatollah Ali al-Sistani, Iraq's top Shiite cleric, later in the day, according to his movement.

Sadr, whose forces led a fierce insurgency against US forces in the years after the 2003 American-led invasion to overthrow Saddam Hussein, had left Iraq at the end of 2006, according to the source in his movement.

The son of revered Grand Ayatollah Mohammed Sadiq al-Sadr, Sadr 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.

The young cleric 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, he 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 of that year.

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.

Despite only rare appearances in public, the cleric is idolised by millions of Shiites, especially in the Najaf where he has his headquarters and the impoverished Baghdad neighbourhood of Sadr City.

Politically, Sadr showed he could pull powerful strings even though out of the country.

After throwing his weight behind Shiite politician Nuri al-Maliki in 2006, ensuring he became prime minister, Sadr then ordered his followers to pull out of the premier's cabinet a year later, almost bringing down the government.

Sadr's bloc contested last year's March 7 legislative election in an alliance with the Islamic Supreme Council of Iraq, another Shiite group with links to Iran.

It won 39 out of the 325 parliamentary seats. The Sadrists were widely seen as "kingmakers" after the inconclusive election.

Sadr said after the polls he had "tried not to have a veto against anyone, but the masses had a veto against Maliki."

But his movement later lifted its veto over Maliki becoming prime minister again, and Sadr threw his weight behind Maliki when the premier was tasked with forming a government following the election.

Sadr's bloc now holds six cabinet posts -- Housing and Construction, Labour and Social Affairs, Water Resources, a minister of state for Tourism and Archaeology, and two ministers without portfolio -- in the national unity cabinet that was approved by parliament on December 21.

Deputy speaker of parliament Qussai Abdel Wahab al-Suhail is a member of Sadr's bloc.

Sadr's father and two brothers were killed in 1999 by gunmen allegedly sent by dictator Saddam Hussein, who was ousted in the US invasion of 2003.