In June, the US Appeals Court in Washington gave Secretary of State Hillary Clinton four months to decide whether or not to remove the Mujahedin-e-Khalq (MEK) – Iran’s largest and best organised democratic opposition group – from the government’s list of foreign terrorist organisations. The State Department has said that it intends to comply with the deadline, which falls on October 1.

The MEK, whose annual rally in Paris this year attracted nearly 100,000 supporters, is an anomaly on the State Department’s blacklist. Added in 1997 by the Clinton administration as a goodwill gesture toward the theocratic Iranian regime, the MEK to this day remains on the US terror list despite its explicit renunciation of violence in 2001 and total voluntary disarmament in 2003.

Even so, the US and its allies have often relied heavily upon information obtained by the MEK’s impressive intelligence-gathering network inside Iran. It was the MEK, for instance, that first exposed Iran’s secret nuclear program in 2002. The latest MEK report, which went public in May, further revealed how a specialist team of 60 nuclear scientists had been assembled to work on an atomic weapons program overseen by Iran’s Revolutionary Guards.

Why, then, is the MEK terror label still in place? Although there is a growing consensus that “evidence” of the group’s involvement in terrorism is nothing more than Iranian propaganda, there is a prevailing belief that the MEK does not command enough support on the Iranian street to mount a successful challenge to the mullahs in Tehran. It is this assumption that has stifled the determination of many in Washington to push for the MEK to be delisted once and for all. But it is an assumption that is very unlikely to be correct.

Historically, the MEK has enjoyed a significant degree of popularity amongst the Iranian population. Such was the threat posed to the regime by the MEK in 1988 that then-supreme leader Ayatollah Khomeini ordered between 15,000 and 30,000 of its members executed. That level of support seems to have endured into the present day, with one study showing that the official Iranian news agency’s coverage of the MEK in one year was 350% greater than all other dissident groups combined. It is unsurprising, therefore, that a majority of the demonstrators arrested and hanged after the anti-government protests of 2009 turned out to be MEK sympathizers.

For those who wish to see regime change in Tehran, there is no viable alternative to the MEK. While the Green Movement – or what is left of it – offers some hope, it is more like a fractured coalition of moderates and reformists than a cohesive opposition movement. Moreover, we ought to remember that its leaders openly accept clerical rule. Only the MEK stands opposed to the theocratic regime. As such, it is Iran’s only hope for democracy.

If the US secretary of state chooses to remove the MEK from the list of foreign terrorist organizations by October 1, she will have legitimized and empowered the Iranian resistance at a stroke. Even those who are sceptical of the potential for regime change cannot deny that Iran will be far more likely to make concessions during negotiations over its nuclear program if its rulers are weakened by a domestic pro-democracy movement with a new lease of life. Sanctions alone are plainly not doing the job.