Unlike PJAK, however, MeK has not committed violent acts in recent years. It has been unable to attack Iran because its main base in Iraq (Camp Ashraf) has been under U.S. control since 2003 and in the Iraqi government's hands since 2008.
Iran and the United States don't agree on much these days, but there are a few views they hold in common.
Both regard the Kurdish Party of Free Life for Kurdistan (PJAK) and the Mujahedin-e Khalq (MEK) or People's Holy Warriors as terrorist organisations.
In the last few weeks, Iranian forces have been shelling PJAK camps and fighters near and across the Iranian border in Iraqi Kurdistan.
According to an Iranian source who has been reliable in the past and who spoke on condition of anonymity, U.S. forces observed the fighting from the air and did nothing to stop it. In fact, the source said, "There was good coordination [between Iran and the United States] to destroy this terrorist organization."
An Iraqi Kurdish official, also speaking on condition of anonymity, disputed the report of U.S. tacit cooperation against PJAK. The official said the U.S. military presence in Iraq is "insignificant" and far from the Iraq-Iran border. He added that the United States would be more inclined to back PJAK because "it's anti-Iran".
Asked if the U.S. had, at a minimum, condoned Iranian attacks on three PJAK camps, however, George Little, the chief Pentagon spokesman, had no comment. He also declined to comment on any possible links between the Iranian Kurdish operation and a recent decrease in attacks on U.S. forces in Iraq by Iran-backed Iraqi Shiite militants.
The world's largest ethnic minority without its own state, Kurds are scattered across mountainous regions of Iran, Iraq, Turkey and Syria. They have the greatest freedom in Iraq, thanks to U.S. protection since the 1991 Gulf War and an autonomous status confirmed after the toppling of Saddam Hussein's regime in 2003.
Patrick Clawson, a Middle East expert at The Washington Institute for Near East Policy, said U.S. tacit approval for the Iranian raids was "entirely plausible" given U.S. opposition to Kurdish militants.
"The U.S. was signaling the KRG [Kurdistan Regional Government] that you can't just let this problem fester," Clawson told IPS. He noted that the PKK or Kurdistan Workers Party, the parent organization of PJAK, had recently intensified attacks in Turkey.
A State Department official told IPS in an email that "PJAK was created in 2004 as a splinter group of the PKK to appeal to Iranian Kurds." The official, who asked not to be named, noted that the PKK was "a designated Foreign Terrorist Organization that has been involved in the targeting of the Turkish government for more than 20 years."
The State Department also regards the MEK - an Iranian opposition group that has about 3,000 members in Iraq - as terrorist but that designation is currently under review and has provoked growing controversy in Washington.
Originally a Marxist-Islamist group that killed Americans in Iran before the 1979 revolution and Iranian officials both before and after the revolution, it has been designated since the terrorist list's inception in 1997. MEK officials insist the group has renounced violence and deserves to come off.
In recent months, MEK supporters have engaged in an aggressive lobbying campaign in Washington that has included a number of events at which former senior U.S. officials have received hefty sums to speak. Among them: ex-FBI chief Louis Freeh, former attorney general Michael Mukasey and former Central Command head Anthony Zinni.
The MEK has scant support within Iran because it sided with Iraq during the 1980-88 Iran-Iraq war. Former members say the organisation is a cult fixated on leader Maryam Rajavi and her husband, Massoud, whose whereabouts are unknown. A State Department official told IPS that "attempts to paint the MEK as the poster child for the democracy movement in Iran are grossly ironic."
Unlike PJAK, however, the group has not committed violent acts in recent years. It has been unable to attack Iran because its main base in Iraq - Camp Ashraf - has been under U.S. control since 2003 and in the Iraqi government's hands since 2008.
One argument used by supporters of de-listing is that it will help resolve the humanitarian plight of MEK members who remain at Camp Ashraf. However, the State Department official said that taking the group off the list would not mean that they could come to the United States.
U.S. law "places a permanent, non-waivable bar to immigration in the way of anyone who has ties to a Foreign Terrorist Organization," the official told IPS. He said this includes "those who provided material support to, or received military-type training from the group, as many MEK members have".
U.S. diplomats have been trying to arrange new homes for the camp residents but have been hampered by the fact that their leaders refuse to accept refugee status.
Maziar Bahari, an Iranian-Canadian journalist and film maker, said the MEK needs to keep the camp to maintain control of its foot-soldiers. He said that U.S. officials feared a "Jonestown in Ashraf" if attempts were made to remove camp residents by force. He was referring to the mass suicide in Guyana in 1978 of hundreds of fanatical followers of a self-styled prophet, Jim Jones.
Bahari, speaking at a conference in Washington Thursday sponsored by the National Iranian American Council, a non-partisan group that advocates for Iranian Americans and opposes the MEK, expressed sympathy for MEK members but said it would be a mistake to take the group off the State Department list at this time.
Given the group's violent past and violent potential, Bahari said, "It would send a very wrong signal [to Iranians] about America's intentions in Iran." He said the MEK was "the perfect opposition" for an Iranian regime seeking to paint peaceful protestors as violent extremists backed by foreigners.
*Barbara Slavin also spoke at the NIAC event but did not advocate keeping the MEK on the terrorist list or removing it. She did question the group's democratic credentials.