Iran did shut down its nuclear weapons program in 2003 but restarted it a year later, moving and hiding the equipment to thwart international inspectors, according to an Iranian opposition group, the Wall Street Journal reported Tuesday.

The group, the National Council of Resistance of Iran exposed the country's nuclear-fuel program in 2002 and now believes a newly released U.S. analysis is giving the wrong impression that Iran's nuclear program is not an urgent threat, the newspaper reported.

The U.S. National Intelligence Estimate published last week said Tehran shut down its weaponization program in 2003, contradicting an earlier report that the Islamic Republic was determined to build a nuclear bomb.

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The NCRI, considered by the United States and European Union to be a terrorist organization, has had a mixed record of accuracy with its claims about Iran's nuclear ambitions in the past, the Wall Street Journal said.

The NCRI, however, says it was added to the EU terrorist list under pressure from Tehran at a time when Western countries were trying to improve relations with Iran.

The group agrees that Iran's Supreme National Security Council decided to shut down its most important nuclear weapons research center in eastern Tehran, called Lavisan-Shian, in August 2003, the Journal said.

But the group, which claims it has sources inside Iran, told the paper the facility was broken into 11 fields of research, including projects to develop a nuclear trigger and shape weapons-grade uranium into a warhead.

"They scattered the weaponization program to other locations and restarted in 2004," Mohammad Mohaddessin, NCRI's foreign affairs chief, told the Wall Street Journal.

"Their strategy was that if the IAEA (International Atomic Energy Agency) found any one piece of this research program, it would be possible to justify it as civilian. But so long as it was all together, they wouldn't be able to."

By the time international inspectors were allowed to visit the Lavisan site, the buildings Iran claimed were devoted to nuclear research had been torn down and the ground bulldozed, the paper reported.

The NCRI said the equipment was moved to another military compound known as the Center for Readiness and Advanced Technology, to Malek-Ashtar University Isfahan and to a defense ministry hospital in Tehran.