Iran will "shortly" face a new deadline and a renewed threat of economic sanctions by the U.N. Security Council if it does not suspend its uranium enrichment program, Undersecretary of State Nicholas Burns said late Tuesday.

Diplomacy surrounding Iran's renegade uranium enrichment program has entered "extra innings" but ongoing talks will not be "endless," Burns said.

Burns briefed reporters after he and Secretary of State Condoleezza Rice attended a two-hour dinner with foreign ministers and political directors from European countries involved in the diplomatic effort with Iran.

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Joining the usual retinue of the permanent members of the U.N. Security Council — the United States, the United Kingdom, France, Russia and China — were Germany, a key member in the negotiations with Iran; Italy's foreign minister Giuliana Sgrena; and European Union foreign policy chief Javier Solana, who has doubled as the group's chief interlocutor with Iranian nuclear negotiator Ali Larijani.

The dinner followed, and marked another chapter in, the ongoing tale of diplomatic maneuvering on Iran. It picked up the story that left off with the report issued on Aug. 31 by the International Atomic Energy Agency, the U.N.'s nuclear watchdog agency, which found Iran was still actively enriching uranium.

The July adoption of U.N. Security Council Resolution 1696 gave Iran an Aug. 31 deadline to suspend its uranium enrichment program or face sanctions following more than a year of desultory European talks with Tehran. But since then, the Bush administration has worked unsuccessfully to persuade other members of the Security Council to enforce the sanctions threat contained in the resolution.

At the same time, administration officials had dismissed Solana's ongoing talks with Larijani as an extraneous, though "laudable," sideshow to the drive for sanctions.

As recently as Sept. 6, State Department spokesman Sean McCormack told reporters, in advance of another session between the E.U. diplomat and the Iranian negotiator: "The Solana-Larijani meeting has no bearing on whether or not we continue down the pathway of seeking sanctions as follow-up to the agreements reached in Paris, Vienna and then in New York. So those two things are separate."

With leaders from Russia, China, and France having all recently — and publicly — expressed their unwillingness to enforce the sanctions threat contained in 1696, Burns switched gears discernibly. He said all in attendance at the dinner affirmed their "very strong support" for Solana's efforts.

"What happened is that, in late August, the Iranians finally got serious" about negotiations, he said, adding that he and his fellow political directors would continue meeting over the next two weeks to see if they can agree on a viable sanctions program if further talks with Tehran prove fruitless.

But Burns acknowledged that efforts to get the permanent five members plus Germany to agree on an immediate first round of sanctions had failed.

"There is currently no agreement on that. We still need to work that out," he said.

Burns doggedly portrayed the administration's sudden enthusiasm for the Solana-Larijani dialogue as the result not of an American diplomatic failure, but of Washington's desire to give diplomacy every last chance to work.

He also emphasized that the administration's newfound willingness to look beyond the Aug. 31deadline contained in the resolution will not last long.

"If Iran does not suspend [enrichment]," said Burns, the Waldorf group agreed "then we will fulfill 1696. We'll adapt sanctions measures … and there will come a time shortly — but I won't put a date on it — when we are going to have to see an unequivocal answer, because there is no unequivocal answer from the Iranian government."

After Burns finished his opening statement to reporters, a senior administration official spoke slightly more candidly on background.

"Our devotion to diplomacy is such, and our sense of realism about how that particular country probably works is such, that we are willing to see Solana through," the official said. The official suggested that Larijani has been hamstrung in his ability to deal effectively with Solana by internal dissension in Tehran. Cited as evidence for this reading was the fact that Larijani, scheduled to arrive in New York last Saturday, was still absent from the city.

"We may be seeing a great debate in Iran about how to react to this proposal," the official said of the Western incentives package. "They have not decided what to do. ... We understand that Iran is not a monolithic political entity. There are lots of voices [there]."

The official said Solana and Larijani will meet again soon, but that channel will be given only a very short period of time in which to produce a "bottom line" response from Tehran to the central demand of the resolution: suspending Iran's uranium enrichment program. "This is not going to be an endless process," the official warned, adding that during the dinner, the participants agreed on "a very specific time frame but we are not going to make it public, for obvious reasons."

Responding to suggestions that Washington's newfound faith in Solana was more the result of obstructionism on sanctions by the United States' supposed partners in the nuclear diplomacy, the official reminded reporters that the U.S. is not interested in imposing sanctions solely for punitive reasons.

"What matters," the official said, "is where we end up, and the way we end up there."

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).