Russian President Dmitry Medvedev admitted to President Obama during their summit meeting last week that American intelligence estimates about the pace of Iran's progress toward nuclear weapons capability have been more accurate than Russia's, a senior U.S. official told FOX News. 

As a result, Moscow is now said to be open to "much more severe" punishment for Tehran if the regime there persists in enriching uranium into 2010.

The disclosures came as part of a wide-ranging discussion about the Obama administration's now-completed policy review on Iran, which has already led to several high-profile overtures to Tehran by Obama and Secretary of State Hillary Clinton. These gestures have included Obama's videotaped greeting marking the Iranian new year holiday of Nowruz, and Clinton's invitation for Iran to attend an international conference on Afghanistan that was held in The Hague on March 31. 

The official, who plays a key role in the administration's Iran policy, requested anonymity because he was not authorized to discuss it publicly.

During their closed-door meetings at London's Winfield House on April 1, Medvedev told Obama, according to the source, that "your assessments have been more right than ours" about how quickly Iran's nuclear program has progressed. Such an admission by the Russian president startled those present, and is significant. 

It shows that Moscow shares the sense of alarm about Iran's nuclear program exhibited by American and Israeli leaders; and it reflects renewed confidence abroad in American intelligence data, which many countries derided in the aftermath of the U.S.-led invasion of Iraq.

In the brief joint appearance before reporters that followed their private meetings, neither Medvedev nor Obama explicitly mentioned Iran. However a senior Obama aide who attended the presidents' private session and who was sent to brief the press about it that same day told reporters, without elaborating, that he was "struck by the agreement about threats from countries like ... Iran." That official added: "(The Russians have) always said Iran is not developing a nuclear weapon -- 'We have no evidence of that, show me that this is there.' And this (meeting between the two presidents) was a different tone than that."

The Obama administration will not unveil its new, integrated Iran policy with a flashy "roll-out" like the one that accompanied the president's major speech on Afghanistan and Pakistan. Instead, senior officials in the National Security Council and State Department are quietly coordinating their intertwined activities, which include remaining alert to opportunities for further engagement with Iran; reassuring Arab states in the Persian Gulf, nervous about Iran's growing clout in the region, that engagement will not come at their expense; and persuading Russia and China that tougher sanctions against Iran will be needed if Tehran continues to reject international demands for a halt to its enrichment of uranium.

"The idea is to affect the landscape that (the Iranians) are looking at," said the source who detailed the new policy to FOX News. "If they look around and see that the Russians won't be their insurance policy any longer, and they know the Gulf states are not going to accommodate them, and some of the Europeans are no longer going to be softer than some others, we might be able to change (the Iranians') calculus. ....We are shoring up the collective response, so that others can be in a position to say to Iran, 'Hey, you have an opportunity here -- don't miss it.'" 

In the event Iran does press forward with enrichment, the Obama administration believes the Russians will, within the next year or so, sign on to tougher sanctions. "We have laid the basis for much more severe consequences," the source said.

The source, who has long experience at the highest levels of Washington's foreign policy and national security apparatus, emphatically rejected claims by some former Bush administration officials who allege that the Obama administration has essentially reconciled itself to a nuclear Iran, and is now readying a "Japan option" for the Islamic republic. Under such a scenario -- so named because of its similarity to Japan's nuclear program -- Iran would be permitted to retain an indigenous enrichment capability, with international monitoring put in place to ensure that Iran's operations do not move from their current, low enrichment of uranium, which is usable in a civilian energy program, to high enrichment, which is suitable for the production of nuclear weapons.

"No way is Japan a model," said the source. "Whoever told you this has absolutely no idea of our approach. ... The outcome (of engagement with Iran) should strengthen the Nuclear Non-Proliferation Treaty. We can't have one more exception to the non-proliferation regime," the source said, in an apparent reference to the Bush administration's decision to recognize India as a member of the nuclear club, despite New Delhi's longstanding refusal to sign the NPT accord. "The Arabs will all want exactly the same thing."

The source spoke on the same day that Under Secretary of State William Burns met in London with other members of the "P5 + 1," a working group on Iranian nuclear diplomacy that includes representatives from the permanent five members of the United Nations Security Council and Germany. The meeting ended with a new agreement by Burns to attend the group's direct contacts with Iranian officials, a form of engagement the Bush administration had largely eschewed. The source told FOX News the next readily visible signal of American willingness to engage Iran will be when Burns and his fellow P5 + 1 diplomats sit down with an Iranian delegation, likely to occur before Iran holds its nationwide elections in June.

By then, three years will have passed since the P5 + 1 first offered Iran a package of incentives and "disincentives" to halt enrichment, which Iran has steadily refused to consider. Asked about reports that the new round of diplomacy will simply sharpen the elements in the 2006 package, the source agreed the old offer will be "refined," with the major powers watching carefully to see Iran adopts what the source called "a rope-a-dope strategy." 

"This can't be open-ended," the source explained, because Iran, if left unchecked, will likely reach a nuclear weapons capability within the next two years. "We don't come with an arbitrary timetable, but at the same time this can't go on forever."

In Iran, President Mahmoud Ahmadinejad said he welcomed the American offer to attend the P5 + 1 sessions. However, on the same day, the Iranian government announced it was filing espionage charges against Roxana Saberi, a U.S.-born freelance journalist with Iranian citizenship who was detained inside the country in January. Clinton said she was "deeply concerned" by Saberi's jailing, adding "we wish for her speedy release and return to her family."

The U.S. official involved in Iran policy told FOX News the "mixed messages" conveyed by Ahmadinejad's conciliatory statement and the filing of charges in the Saberi case reflected internal disagreements within the Iranian regime over how to respond to Obama's new tactic of engagement. 

"It was easier for them when they could portray Bush as (hostile)," the source said. "They are grappling right now. ...They've never before felt on the spot to make choices. And they're already uncomfortable."

James Rosen joined Fox News Channel (FNC) in 1999. He currently serves as the chief Washington correspondent and hosts the online show "The Foxhole." His latest book is "A Torch Kept Lit: Great Lives of the Twentieth Century" (Crown Forum, October 4, 2016).