In the final hours of Iran's fierce election campaign, the top pro-reform challenger to President Mahmoud Ahmadinejad got a sharp warning that authorities would crush any attempt at a popular "revolution" inspired by the huge rallies and street parties calling for more freedoms. The threat made Wednesday by an official of the powerful Revolutionary Guard reflected the increasingly tense atmosphere surrounding Friday's up-for-grabs election. It also marked a sharp escalation by the ruling clerics against the youth-driven campaign of Mir Hossein Mousavi and its hopes of an underdog victory. The Revolutionary Guard is one of the pillars of the Islamic establishment and controls large military forces as well as a nationwide network of militia volunteers. The message from the Guards' political chief, Yadollah Javani, appeared to carry twin purposes: to rattle Mousavi's backers just before the polls and to warn that it would not tolerate the formation of a post-election political force under the banner of Mousavi's "green movement" - the signature color of his campaign. In a statement on the Guards' Web site, Javani drew parallels between Mousavi's campaign and the "velvet revolution" that led to the 1989 ouster of the communist government in then-Czechoslovakia. "There are many indications that some extremist (reformist) groups, have designed a colorful revolution ... using a specific color for the first time in an election," the statement said. Calling that a "sign of kicking off a velvet revolution project in the presidential elections," Javani vowed that any "attempt for velvet revolution will be nipped in the bud." Javani also accused the reformists of planning to claim vote rigging and provoke street violence if Mousavi loses. Ahmadinejad is believed to have wide support in the Revolutionary Guard and among Iran's ruling clerics, though neither have given public endorsements in a presidential race that has seen the sudden and unexpected rise of Mousavi, who served as prime minister in the 1980s. There was no immediate reaction from Mousavi or his campaign, and no public rallies or speeches are allowed the day before Friday's vote. Tens of thousands of Mousavi supporters remained in the streets, dancing on cars, waving green flags and passing pro-Mousavi fliers into car windows into the wee hours Thursday, just before the official end of campaigning. The lingering images from the campaign's final hours summed up the intensity of the past weeks. Ahmadinejad drew tens of thousands of flag-waving backers, including many women in black Islamic chadors, as he claimed he was the victim of Nazi-style propaganda. Mousavi's backers staged a huge march through central Teheran waving the campaign's trademark color, green. "They applied the methods of (Josef) Goebbels, propaganda minister of Hitler," Ahmadinejad told supporters jamming a street for one of his last appearances before the vote. "They used this method of psychological war against our nation." It was an apparent reference to Ahmadinejad's repeated claims that Mousavi has exaggerated Iran's economic problems to discredit the government. Mousavi has dismissed his rival's charges as an attempt to whitewash the scope of Iran's problems, which include double-digit inflation and chronic unemployment. Mousavi has also criticized Ahmadinejad for blackening Iran's international reputation by questioning the Holocaust and calling for Israel's destruction. Mousavi's backers poured into the streets in Teheran Wednesday in a last display of political might that has included all-night street rallies that have rekindled the passions and hopes of reformists after Ahmadinejad's victory four years ago. Their calls are similar to the days of reformist President Mohammad Khatami - more social freedoms, media openness and outreach to the West. But now there are some potentially groundbreaking stakes, including how to respond to President Barack Obama's offer for dialogue with Iran after a nearly 30-year diplomatic chill. The election outcome will have little direct impact on Iran's key policies - including its nuclear program or possible talks with Washington - which are directly dictated by the ruling Islamic clerics. Still, the president has influence over some domestic affairs, such as the economy, and serves as Iran's highest-ranking envoy on the international stage. Ahmadinejad has become a deeply polarizing figure and Mousavi has promised a softer approach to the West. His proposals include creating an international consortium to oversee uranium enrichment in Iran. The United States and others fear Iran could eventually seek nuclear weapons; Iran says it wants only peaceful reactors for electricity. "The election is important to gauge the direction of the country," said Nicholas Burns, a former No. 3 diplomat at the State Department who was involved in US policy-making on Iran. "Iran's international reputation has diminished greatly under Ahmadinejad. The ruling establishment has been waiting for these elections to be over before answering Obama's call for dialogue. I think once this is over, we will see the beginning of negotiations." As the campaign wound down, Ahmadinejad made one final push in Teheran while Mousavi visited rural mountain areas in western Iran that are considered strongholds of conservative support. At a rally in Teheran, Ahmadinejad's backers cried "Mousavi is a liar!" and "Mousavi bye-bye" - a take on the "Ahamdi bye-bye" that's become a staple of opposition rallies calling for Ahmadinejad's ouster. Women in long black robes wore Iranian flags tied around their necks or underneath their head covering. Mousavi has made Iran's struggling economy a hallmark of his campaign, accusing Ahmadinejad of manipulating statistics that hide the extent of the nation's fiscal problems despite its vast oil and gas reserves. Earlier this week, Ahmadinejad insisted inflation stood at 15 percent - lower than the 25 percent widely reported by financial officials. On Tuesday, Ahmadinejad acknowledged that inflation was 25 percent. Two other candidates are in the race: former Revolutionary Guard commander Mohsen Rezaei and former parliament speaker Mahdi Karroubi. In the increasingly tight race, their level of support could play a swing role - with Rezaei expected to draw conservative voters and Karroubi pulling in moderates.