U.S., ALLIES POINT TO SECRET IRANIAN NUKE FACILITY…. A big story out of Pittsburgh this morning.

President Obama and the leaders of Britain and France accused Iran on Friday of building a secret underground plant to manufacture nuclear fuel, saying the country hid the covert operation from international weapons inspectors for years.

The revelation, which the three leaders made before the opening of the Group of 20 economic summit here, adds urgency to the diplomatic confrontation with Iran over its suspected ambitions to build a nuclear weapons capacity. Mr. Obama, flanked by Prime Minister Gordon Brown of Britain and President Nicolas Sarkozy of France, demanded in a Friday morning news conference that Iran allow the International Atomic Energy Agency to conduct an immediate inspection of the facility, which is said to be 100 miles southwest of Tehran.

“The existence of this facility underscores Iran’s unwillingness to cooperate” with international rules governing peaceful nuclear development, Mr. Obama said. “The Iranian government must now demonstrate in deeds its peaceful intentions, or be held accountable,” he said.

Brown added that Iran’s “level of deception … will shock and anger the whole international community.”

The Iranian facility, built inside a mountain 100 miles southwest of Tehran, has been on American officials’ radar for years, but is not yet in operation. Iranian officials realized this week that the secrecy surrounding the facility had been breached, so they quietly told the IAEA, in a brief and vague letter, about a “pilot plant” it’s building. Iran insists its up-until-recently secret site has peaceful purposes; President Obama said this morning that its size and capabilities suggest otherwise.

This morning’s remarks are intended, not only to press Iran and press the IAEA to act, but also to help lay the diplomatic groundwork for sanctions against Iran, which Ahmadinejad has made easier by getting caught lying.

Of particular interest is Russia, which has been more than a little reluctant to punish Iran. Obama spoke at length to President Dmitri Medvedev about Iran, and given Russia’s new found satisfaction with the U.S. administration — Obama’s move away from the Bush-era missile-defense policy was extremely well received — Russia’s leadership is now reportedly far more open to sanctions against Iran. Indeed, Medvedev seems to consider sanctions “inevitable.”

That’s a significant shift from Russia’s previous position, and suggests President Obama’s strategy in improving relations with the country is paying valuable dividends.

As for the next step, the IAEA is demanding additional information. Just as important, next week in Geneva, representatives of the permanent members of the U.N. Security Council, Germany, and Iran will meet, and Obama noted this morning that there’s now an increased “sense of urgency” surrounding the discussions.

Update: A good item from Marc Lynch on the strategy behind this morning’s announcement.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.