Here is an article from which I have excerpted the salient explanation for Adm. Mullin's statement:

THE WALL STREET JOURNAL

REVIEW & OUTLOOK MARCH 4, 2009 Obama's Iran Crisis

It's arriving faster than he thinks.

As a Presidential candidate, Barack Obama called a nuclear Iran "a grave threat" and said "the world must prevent Iran from obtaining a nuclear weapon." But he also called for direct, high-level talks in the hopes that the mullahs could be persuaded to abandon their nuclear dreams.

We've never held out much hope for those talks, which would inevitably be complicated and protracted. Mr. Obama is already trying to lure Russian help on Iran by offering to trade away hard-earned missile defense sites in Eastern Europe. Russia's President claims to be unimpressed. And now it turns out that the rate at which Iran's nuclear programs are advancing may render even negotiations moot.

That's a fair conclusion from the latest report by the U.N.'s International Atomic Energy Agency. Among other disclosures, the IAEA found that Iran has produced more than 1,000 kilograms of low enriched uranium (LEU), enough for a single bomb's worth of uranium after further enrichment. The IAEA also found that Iran had underreported its stock of LEU by about 200 kilograms, which took the agency by surprise partly because it only checks Iran's stockpile once a year. This is the basis for Chairman of the Joint Chiefs Michael Mullen's weekend acknowledgment that the U.S. believes Iran has enough fissile material to make a bomb.

Iran now possesses 5,600 centrifuges in which it can enrich uranium -- a 34-fold increase from 2006 -- and plans to add 45,000 more over five years. That will give Tehran an ability to make atomic bombs on an industrial scale. Iran has also announced that it plans to begin operating its Russian-built reactor at Bushehr sometime this spring. That reactor's purposes are ostensibly civilian, but it will eventually produce large quantities of spent fuel that can covertly be processed into weapons-usable plutonium.

That's not all. The IAEA says its inspectors have been denied access to a heavy water reactor in Arak, and that Iran has put a roof over the site "rendering impossible the continued use of satellite imagery to monitor further construction inside the reactor building." Most proliferation experts agree that the Arak reactor, scheduled for completion in 2011, can have no purpose other than to produce weapons-grade plutonium.

True to form, Iran continues to deny the IAEA access to other parts of its nuclear programs, including R&D facilities and uranium mines. "Regrettably," says the report, "as a result of the continued lack of cooperation by Iran in connection with the remaining issues which give rise to concerns about possible military dimensions of Iran's nuclear programme, the Agency has not made any substantive progress on these issues."