On one side is an Iranian group officially listed as a terrorist organization -- anti-government activists linked to kidnapping and assassinations of Iranians and Americans over several decades.

On the other are Americans and Israelis, saber-rattling in a bid to prevent Iran from developing nuclear weapons but who have stopped short of supporting a military strike on the country's uranium-enrichment facilities.

Could the terrorists be the advance guard for the West -- the proxy in-country soldiers who will do the dirty work for the United States and its ally Israel?

The People's Mujahedin of Iran -- known variously as the PMOI, Mujahedin-e-Khalq and MEK -- was a left-wing militant group before Iran's Islamic revolution and overthrow of the shah in 1979. Now it's an exiled political entity based in neighboring Iraq whose stated mission is to topple the regime of Iran's supreme leader, Ayatollah Ali Khamenei.

MEK has been getting publicity of late, with numerous American politicians, liberals and conservatives alike beating the drum for its removal from the State Department list of terrorist organizations. In practice, the designation means no U.S. companies or citizens can give MEK money or do business with the group. The argument most supporters give is that MEK has reformed into a democratic organization and is no longer a threat to U.S. interests.

Some MEK backers may be motivated by money. Former Pennsylvania governor Ed Rendell and a former chairman of the Joint Chiefs of Staff, Gen. Hugh Shelton, are under investigation by the Treasury Department for accepting as much as $150,000 from MEK to lobby for delisting in speaking engagements.

Other prominent politicians and officials, including former homeland-security chief Tom Ridge, ex-New York mayor Rudolph Giuliani and former NATO commander Gen. Wesley Clark have also participated in events or written articles supporting MEK's removal from the terrorist list. These activities were paid for by the group's political arm, the National Council of Resistance of Iran, and various Iranian-American cultural organizations.

But throughout the ongoing discussion about MEK and its motives and political ties, one possibility has flown under the radar: that the United States and Israel may already be paying clandestine MEK operatives to destabilize Iran's nuclear program.

On the premise that the enemy of my enemy is my friend, funding, arming or training MEK is an important strategic tool for Israel and the U.S., said Dilshod Achilov, assistant professor of Middle East politics at East Tennessee State University.

The operatives of MEK and PJAK [Party of Free Life of Kurdistan] are seen as invaluable agents for [Israeli and U.S. spy agencies] Mossad and CIA because they can work covertly inside Iran and carry out various tactical missions rather discreetly. There is little doubt that MEK is actively involved in sabotaging, either directly or indirectly, the Iranian nuclear program, he said.

In what experts say is the most likely scenario, MEK has played a key role in the assassination of four Iranian nuclear scientists. The latest of these occurred in January when Mostafa Ahmadi Roshan, a university chemistry professor who doubled as a director of Iran's Natanz uranium-enrichment facility, was killed after two assailants on a motorcycle attached a magnetic bomb to his Peugeot 405.

Roshan's killing was nearly identical to a November 2010 attack in Tehran in which nuclear engineer Majid Shahriari died and Fereydoon Abbasi Davani, head of Iran's Atomic Energy Organization, was wounded.

In addition, intelligence specialists have linked MEK and Mossad to an explosion at a Revolutionary Guard base about 30 miles west of Tehran last November; the blast killed 17 people including Maj. Gen. Hassan Tehrani Moqaddam, Iran's most senior missile commander. Also in 2011, Iranian uranium-enrichment facilities were attacked by a highly sophisticated computer virus called Stuxnet that reportedly disrupted and spied on Iran's nuclear program.

MEK is a gun for hire, said Trita Parsi, founder of the National Iranian American Council, a nonpartisan community organization based in Washington. They continue to exist as long as they have a patron to pay for them to do what they do best ... and there seems to be that desire in Israel.

They will do almost anything that they are being paid to do, Parsi said. Not too long ago this organization was conducting terrorism for Saddam Hussein.

In February, two anonymous Pentagon officials told NBC News that Israel's Mossad has been funding MEK for at least five years and training the group's operatives to carry out assassinations of nuclear scientists. Confirming statements made by Mohammed Javad Larijani, a senior aide to Iran's Khamenei, the officials said the United States is aware of but not involved in the relationship between Israel and MEK.

Israel does not have direct access to our society, Larijani told NBC News in conjunction with that February report. Mujahedin, being Iranian and being part of Iranian society, they have ... a good number of ... places to get into touch with people. So I think [Israel] is working hand-to-hand very close. And we do have very concrete documents.

Israel's Foreign Ministry, which has yet to deny responsibility for the recent assassinations, dismissed the alleged MEK connection as gossip, and MEK, which was stripped of its weapons after the U.S. invasion of Iraq in 2003, has denied any involvement in the killings.

Attributing murder of the mullahs regime nuclear scientist to the PMOI is absolutely false, the group said in a statement.

Instead, MEK asserts that the Iranian regime is guilty of killing its own scientists. There is a special unit of the Revolutionary Guard, the group claims, that's responsible for killing any nuclear expert who tries to break with the program or leave Iran. MEK, Israel and the United States are then framed for the crime, the conspiracy goes.

However, Richard Silverstein, a longtime journalist in the Middle East with sources in the Israeli intelligence community, calls MEK's relations with Mossad one of the worst-kept secrets of the war between Israel and Iran.

It is widely known within intelligence circles that the Israelis use MEK for varied acts of espionage and terror ... [including] assassinations of nuclear scientists and bombings of sensitive military installations, Silverstein claimed on his Israeli-security blog Tikun Olam.

According to Silverstein, the alleged Mossad-MEK relationship is directly tied to the Iran strategy of the CIA, which is funneling money to MEK through Mossad. As an example of this arrangement, Silverstein points to $400 million allocated by President George W. Bush in 2007 for CIA and Special Forces operations to undermine Iran's nuclear program and leadership. Other experts agree and see the value that Americans are getting for this money in the effectiveness of MEK's alleged subterfuge in Iran.

The level of sophistication of the attacks suggests that the perpetrators are well-equipped, well-informed and thus have not been acting alone, said Achilov, the Middle East scholar.

Even if the United States isn't secretly backing MEK, whether it should provide direct support to the group is moot, geopolitical experts say.

Here is an organization that opposes the autocratic regime and calls for a secular Iran, said Rachel Ehrenfeld, director of the right-wing American Center for Democracy. It's incredible that they are still around, and we should use everyone who can undermine the regime.

To some, this is a dangerous stance to take, particularly because for all its recent pronouncements about establishing a secular democracy in Iran, MEK was founded as an Islamist-Marxist organization and is historically anti-Western. In the early 1970s, MEK was allegedly complicit in the failed kidnapping of U.S. Ambassador to Iran Douglas MacArthur II in 1971 and the killing of the U.S. Army's comptroller, Lt. Col. Louis Lee Hawkins, in Tehran. In 1979, the group supported the takeover of the U.S. Embassy during Iran's Islamic revolution.

They always pursue their own specific interest, said Masoud Banisadr, a former U.S. spokesman for MEK. Banisadr left the group in 1996, or as he put it, escaped. He regards MEK as more a dangerous cult than a terrorist organization and fears the United States will ultimately be hurt by cozying up to it.

They might be useful in one occasion or another, but as a whole as they are not loyal toward any norms, ethics, principles or mutual agreement, Banisadr said. Like al Qaeda, they cannot be trusted.

Considering how dangerous, complex, sensitive and fraught with potential failure a direct attack by Israeli or U.S. forces on Iran would be, Banisadr's warning could fall on deaf ears: Good or evil, MEK may turn out to be the West’s best option for avoiding all-out war.