After a brief wave of optimism, nuclear talks with Iran slowed as senior inspectors from the U.N. nuclear watchdog said they had made no progress in gaining access to Iranian restricted sites suspected of being used to test potential triggers for nuclear warheads.

On one hand, Iran's chief nuclear negotiator stated the next round of talks, set to open June 18-19 in Moscow, could end in failure. On the other hand, EU officials announced that Iran agreed to discuss a proposal from the six world powers to curb production of high-grade uranium in Moscow, seemingly de-escalating tensions ahead of the talks.

Irrespective of the flip-flopping by Tehran, the story behind the story is how the international community gains information on such sites: Iranian nuclear intelligence comes from a variety of sources, including Tehran's opposition.

In December 2005, one dissident group, the National Council of Resistance of Iran, revealed a nuclear site near the city of Qom: Tunneling activity in mountains near Qom was initiated in 2000 with the goal of constructing an underground nuclear facility; the United States and its allies publicly acknowledged the Qom site in 2009. The NCRI revealed in September 2009 two additional sites in and near Tehran; there, the Iranian regime may be working on detonators for nuclear warheads.

In a seemingly unrelated story, which was the main input to calls for congressional inquiries, The New York Times reported that upon coming to office in 2009, U.S. President Barack Obama gave the order to speed up a wave of cyberattacks against Iran. The article states, "Tehran sensed this vulnerability, resumed enriching uranium at an underground site at Natanz, one whose existence had been exposed just three years before." The Washington Post, however, credited, "An exiled opposition group, the National Council of Resistance of Iran, [which] first publicly revealed the existence of Iran's much larger uranium facility at Natanz in 2002."

But the NCRI and its largest unit, the Mujahedin-e-Khalq, are designated on the U.S. terrorist list, although the U.S. judiciary increasingly sees the listing as illegal; similarly, former U.S. Attorney General Michael Mukasey in the George W. Bush administration finds the designation both unwarranted and unwise. And President Bush even credited the NCRI with revelations that led to inspections of and sanctions against Iran.

The ill-advised designation diverts MEK resources from undermining the regime internally and collecting intelligence to struggling with consequences of designation. Although constrained, the resistance has made blockbuster revelations that helped make the case for international sanctions against Iran. The Center for Strategic and International Studies states, "The National Council of Resistance of Iran revelations about Iran's secret nuclear program did prove to be the trigger point in inviting the IAEA into Tehran for inspections ..."

In August 2002, the NCRI exposed a secret nuclear facility near Natanz. An independent think tank, the Institute for Science and International Security, confirmed the revelation, identified the site as a uranium enrichment facility, and released imagery of Natanz in December 2002.

The NCRI made several other critical revelations, including:

-- August 2002, a heavy water production facility at Arak

ISIS stated, "The existence of this facility was first revealed publicly by the Iranian opposition group, National Council of Resistance of Iran, in August 2002. ISIS then located the site in commercial satellite imagery after a wide-area search. By U.N. Security Council Resolution 1737 (2006), Iran was to suspend all work on heavy water related projects."

-- A nuclear facility at Lavizan-Shian

Again working independently from the NCRI, the ISIS wrote: "This site first came to public attention in May 2003 when the Iranian opposition group, National Council for Resistance of Iran, announced … the site."

-- August 2004 laser enrichment facility at the Center for Readiness and New Defense Technology (known as Lavizan 2), built with equipment removed from the Lavizan-Shian site, kept off limits to international inspectors since its revelation by the NCRI.

Regarding the validity of these Iranian resistance revelations, Frank Pabian, senior nonproliferation analyst at the Los Alamos National Laboratory in New Mexico, stated: "They're [the NCRI] right 90 percent of the time. That doesn't mean they're perfect but 90 percent is a pretty good record."

Even if the NCRI and MEK didn't have such an impressive track record, intelligence, especially that from resistance sources, is at least a "lead" to compare with information using other sources and methods.

Regarding sources of intelligence revelations, a U.S. Federal Court informed the U.S. State Department that the court will delist the MEK (and the larger coalition, NCRI) unless State acts to continue the listing or remove it before Oct. 1.

The bottom line is that the MEK designation hampers the resistance from pursuing its opposition against the Iranian regime and harms intelligence collection on Tehran's nuclear progress, let alone cyberattacks and military operations against Iran.

(Raymond Tanter served on the White House National Security Council senior staff in the Reagan-Bush administration and is professor emeritus at the University of Michigan.)

(United Press International's "Outside View" commentaries are written by outside contributors who specialize in a variety of important issues. The views expressed do not necessarily reflect those of United Press International. In the interests of creating an open forum, original submissions are invited.)