Pakistan, North Korea and a former weapons scientist from the Soviet Union reportedly all helped Iran with its nuclear weapons quest, according to an impending U.N. nuclear watchdog report expected to show the Islamic regime has mastered the science of building a bomb. 

The International Atomic Energy Agency's report due out this week will lay out findings collected over years of intelligence gathering. It is expected to reinforce concerns that Iran didn't actually abandon its weapons-related research in 2003, as indicated by a 2007 National Intelligence Estimate given to then-President George W. Bush.

U.S. intelligence agencies reported in 2007 that they believed Tehran halted its experiments in response to international and domestic pressures. But an ongoing investigation by the Fox News Specials Unit concludes that more than 600 entities were working inside Iran to support its program, and at least 40 sites where the work is taking place are suspected to exist across the country. 

For British, French and American investigators, one of the most concerning sites is the Qom uranium enrichment construction site, hidden deep in the mountains. The latest intelligence shows that security walls have doubled around the site. Its scale cannot be explained by any known civilian nuclear energy use.

David Albright, a former IAEA official and president of the Washington-based Institute for Science and International Security who reviewed the intelligence files, told The Washington Post that Iran's nuclear weapons program "never really stopped" and also concluded that Iran "has sufficient information to design and produce a workable implosion nuclear device."

Western diplomats and nuclear experts briefed on the findings in the IAEA report also told the Post that foreign scientists offered assistance in overcoming key technical hurdles.

The documents reportedly show that a former Soviet weapons scientist named Vyacheslav Danilenko allegedly tutored Iranians for several years on building high-precision detonators needed to trigger a nuclear chain reaction. The Post reported that Pakistani and North Korean officials also gave to Iran mathematical formulas and codes as well as a so-called neutron initiator, which shoots a stream of atomic particles into the weapon's fissile core at the start of the chain reaction.

On Monday, U.S. officials cautioned against reaching sweeping conclusions before the report is issued, adding that Iran doesn't have the bomb, and the decision to acquire it will be a political decision.

Some U.S. arms-control groups have also cautioned against overreaction to the report as well as Texas Rep. Ron Paul, a 2012 Republican presidential candidate, who told "Fox News Sunday" that the U.S. is taking the wrong approach to dealing with Tehran. He said the U.S. response to Iran's nuclear pursuits is an "overreaction." 

"The Iranians can't make enough gasoline for themselves. For them to be a threat to us or to anybody in the region I think is just blown out of proportion. People are anxious to use violence against the Iranians. I think it would undermine our security. I think it would be very destructive to Israel because this is going to blow that place up," Paul said.

But former Secretary of State Condoleezza Rice said Sunday that Iran's leaders have lost all "legitimacy" and Iran should be stopped by any means necessary.

"I think it's time to confront the Iranian regime, because it's the poster child for state sponsorship of terrorism. It's trying to get a nuclear weapon. It's repressed its own people," she told ABC. "We should be doing everything we can to bring it down and never take military force off the table."

Iran so far has been dismissive of the IAEA report as it insists that its nuclear program is for domestic energy. Iranian scientists work across multiple disciplines, which can be explained away as part of a civilian nuclear program.

Israel has suggested that it could take action to stop Iran -- as it did with an Iraqi facility in 1981 and a Syrian plant in 2008.