Ayatollah Mohammad Baqir al-Hakim condemned religious extremism in the same speech. He rejected any foreign-installed government for Iraq, but did not mention the United States directly.
Al-Hakim heads the Supreme Council of the Islamic Revolution of Iraq which, reports CBS News Correspondent Elizabeth Palmer, counts among its followers some of the most fundamentalist Muslims in Iraq.
He rolled across the Iranian frontier into Iraq at the Shalamjah border crossing. Al-Hakim had been in exile in Iran and under protection of its Shiite religious leaders since 1980.
"I am a soldier of Islam, serving all the Iraqi people," he told a crowd of about 10,000 supporters hours later in the southern city of Basra, a Shiite stronghold. But, he added, "We don't want extremist Islam, but an Islam of independence, justice and freedom."
But, notes Palmer, his promises ring hollow to both non-Shiite Iraqis and the Bush administration, who point to the 23 years al-Hakim spent in exile close to the radical mullahs in Iran and sending armed militia back from Tehran to organize support in Iraq.
Washington is wary of any Iranian-style theocracy taking control in Iraq, and is particularly jittery about the possibility that a democratic vote might produce a conservative, Islamic-oriented government with close ties to Iran's anti-American Shiite clerics. Washington has accused Tehran of meddling in Iraqi affairs.
In other developments:
Al-Hakim's group, whose English acronym is SCIRI, wants Iraq's future to be governed by Islamic law. He has said in recent days that SCIRI seeks to "realize the will of the Iraqi people," rebuild the country and establish good relationships with neighbors.
The group has made its rejection of American dominance clear: It boycotted the first major U.S.-led meeting near Nasiriyah last month to pave the way for a new administration.
Many have compared al-Hakim's return to that of Ayatollah Ruhollah Khomeini, who spent 14 years in exile in Iraq before returning to lead Iran's 1979 Islamic revolution and lead its clerical regime until his death in 1989.
At the border, about 2,000 supporters, including some clerics, gathered through the morning with the green flags of Islam and portraits of al-Hakim. When he finally crossed into Iraq midmorning, they swarmed his car, climbed upon it and chanted: "Yes, yes, Islam! Yes, yes, al-Hakim!" and "We sacrifice our blood for al-Hakim."
As his 100-vehicle convoy rolled off toward Basra, some threw flowers at it and fervent men threw themselves at al-Hakim's car.
The Shiite sect of Islam, a minority in the Islamic world, represents a 60 percent majority in Iraq and was persecuted and oppressed under Saddam's Sunni Muslim-dominated regime.
Correspondent Palmer says if all Shiite Muslims were united, they could dominate politics in a newly democratic Iraq. But she says they're already divided into factions sparring for control. Hakim portrays himself as the man to bring them together but, adds Palmer, his return could spark infighting that would leave the Shiites nearly as marginalized as they were under Saddam.
SCIRI opposes a U.S. administration in Iraq but has close ties with the rest of the U.S.-backed opposition, including the Kurds and the London-based Iraqi National Congress.
The council's military wing, the Badr Brigade, which the group claims has several thousand fighters, has operated secretly for years in Iraq against Saddam's rule. The fighters have been ordered not to confront U.S. forces.
The Mujahedeen Khalq's well-armed force, which for years fought Iran's Islamic rulers from Iraq with the backing of Saddam Hussein's regime, posed a potential challenge to the U.S.-led coalition's authority as Iraq's military occupier.
The Mujahedeen Khalq's weaponry will be consolidated into one area, and its members will be located in another. They will be "protected by American forces," one military official said. A rival armed group backed by the Iranian regime is active in the area, and there have been fears the two would clash.
Saturday's capitulation, which appeared nonetheless to be a surrender in everything but terminology, underscores the U.S. desire to be the unquestioned and unchallenged armed force in Iraq a month after Saddam Hussein's regime fell.
Its announcement of the Mujahedeen Khalq developments was accompanied by a warning to any groups that might assert authority in postwar Iraq.
"Groups who display hostile intent or refuse to cooperate with the authority of the coalition will be subjected to the full weight of coalition military power," V Corps said. "These groups are urged to submit to the authority of the coalition immediately."