This week Americans observed the 7th anniversary of the worst attack on U.S. soil in our nation's history with memorial services for the 3,000 of our countrymen who perished on September 11, 2001. This week's commemorations should also remind us that the failure to act against a clear and present danger can have extremely dire consequences. That's what happened for eight years with Usama bin Laden's Al Qaeda movement. Unfortunately, it's now happening again with Tehran.

In February 2006, I interviewed Dr. David Kay, the internationally respected arms expert, for a FOX News "War Stories" documentary on the Manhattan Project. Doctor Kay headed the U.N. inspection team after the 1990-91 Gulf War that uncovered Saddam Hussein's nuclear weapons program. During the course of our discussion, I asked Dr. Kay if we should be concerned about Iran's nuclear ambitions. His response was a warning:

"We should be worried about it for two reasons: They're on a course that will in fact finally at some point produce nuclear weapons, and secondly, they have a regime which does not appear to play by the normal rules of stable international behavior. They speak of destruction. They speak of chaos, wiping Israel off the face of the earth. They also are the leading state sponsor of terrorism… not exactly what I view as a secure holder of the nuclear genie."

Last December, a highly controversial U.S. National Intelligence Estimate (NIE) concluded that the Iranians had put their nuclear weapons program "on hold" — perhaps as early as 2003. But this week, in the September/October issue of the National Interest, Dr. Kay proffered yet another caution: "It looks as if Iran is 80 percent of the way to a functioning nuclear weapon."

The evidence Dr. Kay cites for the progress Tehran is making in developing an atomic weapons arsenal ought to be alarming to policy makers in Washington. His sobering assessment: "Iran is pushing toward a nuclear-weapons capability as rapidly as it can," ought to inspire concerted action by the U.S. and our allies to prevent such an outcome. Yet, American and European officials seem content to rely on "voluntary" sanctions imposed by the United Nations.

This week, the U.S. Departments of State and Treasury announced that the U.S. assets of the Islamic Republic of Iran Shipping Lines (IRSL) and more than a dozen of its subsidiaries have been frozen. According to Stuart Levey, undersecretary of the Treasury for counter-terrorism and financial intelligence, IRSL has engaged in a broad "pattern of deception and fabrication that Iran uses to advance its nuclear and missile programs." Treasury officials are also urging maritime insurers to stop providing coverage for Iranian vessels — to include Tehran's fleet of petroleum tankers.

While such measures appear helpful to the goal of preventing Iran from acquiring nuclear weapons, the U.N.-endorsed financial sanctions have thus far had no apparent affect on the ayatollahs' atomic aspirations. Further, diplomats gathering in advance of this month's annual United Nations General Assembly gabfest in New York are grumbling that it is far from certain that the U.N. will take action against insurers of vessels calling on Iranian ports. And of course, all of this is moot if China and Russia continue to do "business as usual" with the Tehran.

The Chinese, wedded to an unimpeded flow of Iranian oil on the world market, are unlikely to back tougher sanctions against Iran in the Security Council. In Moscow, Russian Prime Minister Vladimir Putin, angered by the prospect of U.S. anti-ballistic missile defenses in Eastern Europe, is looking for ways to counter American military superiority. This week he dispatched two Russian Air Force Tu-160 strategic bombers on a "training mission" to Venezuela. He also promised Hugo Chavez, the Marxist despot ruling in Caracas, that Russian Navy units will exercise in the Caribbean. Mr. Putin had already agreed to sell advanced Russian air-defense systems to Iran and Syria.

We know that Russian scientists and engineers built the Iranian nuclear reactor at Bushehr — and that the regime in Tehran has an apocalyptic vision of a confrontation with the West. What we don't know is what new steps the Kremlin may take to accelerate Iran's nuclear program.

If the 9/11 attack is evidence of anything besides the suicidal animus of Islamic radicals toward the U.S., it is also proof that what we don't know can be very dangerous. What we already know about the Iranian nuclear program is frightening enough. What we don't know about it is downright terrifying. Taking steps to stop Tehran from acquiring nuclear weapons should not have to wait until a new administration in January. Dr. Kay is right when he says, "It's got to be our number one priority, not the 'nice to do' if we can get around to it."

Oliver North hosts War Stories on FOX News Channel and is the author of the new best-seller, "American Heroes: In The War Against Radical Islam." He has just returned from assignment in Afghanistan.