The conclusions of a secret U.N. nuclear agency document leaked six years ago were explosive. Iran, it said, had likely worked on developing an atomic bomb.

Two years later the agency went public. It detailed a list of alleged activities based on "credible" evidence that Tehran did work "relevant to the development of a nuclear explosive device."

This week, the bitter debate that for years pitted Iranian denials against U.S. claims of a cover-up appears set for an anticlimactic ending, with a final report from the U.N.'s International Atomic Energy Agency expected to stop short of proving or disproving the claims.

And Washington? It now has opted to let bygones be bygones as it focuses on curbing Tehran's future weapons-making prowess.

The U.S. has long urged that Iran not only trim its present nuclear program but also admit to what it says was past nuclear weapons work. Iran's refusal to address those demands led since 2006 to a series of U.N. Security Council resolutions and sanctions against Tehran — and until recently the latent threat of U.S, and Israeli military strikes against Iran's nuclear facilities.

Those threats have diminished — and Washington's priorities have shifted — with the signing of a July 14 nuclear deal the U.S. engineered with the Islamic Republic. That deal commits Iran to cutting back for more than a decade on nuclear technologies that could be used for weapons-making in exchange for sanctions relief.

But Tehran has warned it might renege if the IAEA report is stacked against it — and Washington now is signaling that it is prepared to shut an eye, even if the threat is no more than bluster.

The long-standing U.S. mantra accused Iran of "deception and deceit," on the weapons issue. As late as mid-June, Secretary of State John Kerry said the IAEA report must "resolve our questions about it with specificity" before any nuclear-related sanctions on Iran are lifted.

Just weeks later, however, Kerry said Washington is not "fixated on Iran specifically accounting for what they did at one point in time or another." Instead, he said the U.S. is concerned about "going forward."

The July 14 deal calls on Iran to "fully implement" the plan with the IAEA to wrap up its investigation. But it only commits Tehran to timetables in providing explanations and information of its own choosing to the agency in time to allow the IAEA to draw up its December report. It says nothing about the kind of information required.

The IAEA's 35-nation board then is scheduled to approve a resolution drawn up by six nations that signed the deal with Iran — the U.S., Russia, China, Britain, France and Germany — that puts the issue to rest.

IAEA chief Yukiya Amano has been careful to diminish expectations, describing his upcoming report last week as "not black and white." Long before he spoke, Iranian officials used those exact words, suggesting they already know that the agency's conclusions won't be damning.

But Iran is not taking chances. With only a day or two remaining before the report's publication, Iranian officials continue to publicly threaten to hold back on commitments to the July 15 deal if the IAEA's assessment is unfavorable to their country.

Two Western diplomats familiar with the issue say those same threats have been made in negotiations with IAEA officials. They demanded anonymity because they are not authorized to discuss the diplomacy.

Iran attaches huge importance to closing the books on the allegations in its drive to lift all punitive measures against it and wipe the slate clean over its nuclear program.

Deputy Foreign Minister Abbas Araghchi made his country's strategy clear in comments apparently published inadvertently and withdrawn shortly after publication in August.

He said his country's threats "will cause the Westerners themselves to pressure the IAEA to wrap up the case as soon as possible, so that the deal could be implemented."

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AP Vienna bureau chief George Jahn has reported on Iran's nuclear program since 2003.