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Pool via AP, Carlos Barria
Iranian Foreign Minister Javad Zarif laughs during a meeting with U.S. Secretary of State John Kerry at a hotel in Vienna, Austria, Tuesday June 30, 2015. Pushing past a deadline, world powers and Iran extended negotiations for a comprehensive nuclear agreement by a week on Tuesday as the U.N. nuclear agency prepared to announce Tehran had met a key condition.

VIENNA — The head of the U.N. agency tasked to monitor a nuclear deal is traveling to Tehran to meet with Iranian President Hassan Rouhani, the agency said Wednesday, as U.S. Secretary of State John Kerry met again in Vienna with Iran's foreign minister.

In his talks in Tehran on Thursday, International Atomic Energy Agency chief Yukiya Amano hopes to "accelerate the resolution of all outstanding issues related to Iran's nuclear program, including clarification of possible military dimensions," the Vienna-based agency said in a statement. Iran's Mehr news agency said Amano will "receive Iran's alternative proposal to nuclear scientists' questioning."

An IAEA probe of the allegations has been essentially stalemated for nearly a decade, with Iran dismissing them as phony evidence planted by the U.S. and Israel.

Washington insists that the agency be given greater powers in its investigations as part of any overall nuclear deal. That includes questioning people possibly involved in the alleged weapons work — something Tehran rejects.

The trip comes as world powers use the seven-day window created by Tuesday's decision to extend negotiations on the nuclear deal amid differences on how much access Iran must give Amano's agency and other disputes.

In their first contact since the extension, Kerry was meeting in Vienna on Wednesday with Iranian Foreign Minister Mohammad Javad Zarif, U.S. officials said.

The State Department announced the extra days of talks only hours before the expiration of the June 30 deadline for their completion. Thoughts of meeting the target had been long-abandoned, but the extension has added significance as it holds in place nuclear restrictions that Iran agreed to some 20 months ago as well as slightly eased conditions for Iranian business with the world.

The June 30 deadline originally had been envisioned as the culmination of almost two years of negotiations aimed at assuring the world Iran cannot produce nuclear weapons, and providing the Iranian people a path of out of their international isolation.

But officials said over the weekend they were nowhere near a final accord, and Iran's foreign minister had briefly flown back to his capital for further consultations amid increased signs of backtracking by his country's supreme leader, Ayatollah Ali Khamenei.

In Washington, President Barack Obama there will be no nuclear deal with Iran if inspections and verification requirements are inadequate.

"I will walk away from the negotiations if, in fact, it's a bad deal," Obama told reporters.

The weeklong extension has political overtones as well. An agreement by July 7 would give the Obama administration time to submit the deal to Congress by July 9. Congress would then have 30 days to review it, during which time Obama would not be able to ease sanctions.

If negotiations drag on past July 9 without a deal, that congressional review period would extend to 60 days. If lawmakers were to build a veto-proof majority behind new legislation enacting new economic sanctions or preventing Obama from suspending existing ones, the administration would be prevented from living up to an accord.

Beyond the level of IAEA inspections on Iranian sites, significant disagreements persist on how quickly the West would roll back sanctions and what types of research and development Iran would be permitted to conduct on advanced nuclear technology.

Associated Press writer Bradley Klapper contributed to this report.