The move came as the American governor of Iraq, L. Paul Bremer, headed to Washington for talks at the White House about several unresolved and thorny issues in the U.S. exit strategy, particularly the transfer of power to a provisional Iraqi government to be concluded by July 1.

The Iraqi council's unanimous decision against the People's Mujaheddin, or MEK, is a significant political and security gain for Iran and could marginalize the group or even eliminate it as an effective opposition movement. The MEK, which was supported by former president Saddam Hussein, has launched hundreds of attacks against Iran over the past two decades.

The move also marks a turning point for U.S. policy. The future of the Iranian opposition group has been heatedly debated within the Bush administration. The MEK, which mixes Marxism and Islam, has been on the U.S. list of terrorist organizations since 1999, but some administration hawks had argued that the group could form the basis for an effort to pressure or change the regime in Tehran.

The administration has been under mounting pressure for months from European and other allies to crack down on the MEK and treat it like a terrorist group, according to U.S. officials and European diplomats. The MEK, born in the 1960s to limit Western influence in Iran and now tied to anti-American attacks, is surrounded by U.S. troops, but it has continued anti-government broadcasts into Iran and other activities.

Washington is prepared to allow the Iraqis to act against the MEK, U.S. officials said yesterday.

The timing is interesting. The Iraqi council's decision comes as Jordan's King Abdullah has been quietly trying to mediate the hand-over of about 70 al Qaeda operatives held by Iran -- in exchange for action by the United States on the MEK.

The move may also be linked to the Iraqi council's efforts to improve relations with Iran, another predominantly Shiite Muslim country that shares Iraq's longest border.

Ahmed Chalabi, a leading council member with close ties to both the United States and Iran, proposed the resolution. A Shiite Muslim, he recently visited Iran, according to Iraqi sources. Most of the 24 Governing Council members have been to Iran in recent months.

The MEK has been spurned by Iraqi Shiites, even though many of its members are Shiites, because Hussein used the Iranian group to help put down the Shiite uprising in southern Iraq after the 1991 Persian Gulf War, according to U.S. officials. Thousands of Iraqis were killed.

The move, which will assuage Iranian concerns, will deprive the MEK of its only direct access to Iran. There are now no major opposition groups operating on any of Iran's borders.

An unanswered question is what will happen to the MEK. The Iraqi council's resolution calls for the closure of the MEK headquarters in Baghdad and a prohibition on its members' engaging in any political activities until their departure. It also calls for the seizure of all MEK funds and weapons, both of which will be turned over to a fund to compensate victims of Hussein's regime.

But the council did not discuss where the group would go. "It's up to them," said Entifadh Qanbar, a senior official of Chalabi's party, the Iraqi National Congress. "They can seek refuge in other places. We don't care where they're going to go."

Qanbar said Iran had offered the MEK an amnesty. The United States, however, will not turn the MEK over to Iran, which is on the State Department's list of state sponsors of terrorism.

Several senior MEK officials fled to Europe shortly before the U.S. invasion. More than a dozen were arrested in France several months ago for plotting terrorist activities.

"It's the same problem as dealing with [former president] Charles Taylor in Liberia. These are really bad guys who have to be dealt with in a fair and transparent way that holds them to account for what they've done. But how that is carried out has yet to be worked out. . . . At the moment they're confined to camps and not doing anyone any harm," a senior State Department official said yesterday.

Iraqis denied that they were pressured by the United States to act. "The council based its decision on the black history of this terrorist organization and the crimes committed against our people and our neighbor," the council said in a statement yesterday.

Chandrasekaran reported from Baghdad.