Iranian media reported the talks will focus on a dispute over interviewing experts alleged to have worked on atomic arms that has spilled over into negotiations on a deal.
In his meetings tomorrow, 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," said an IAEA statement.
Iran's Mehr news agency said Amano will "receive Iran's alternative proposal to nuclear scientists' questioning."
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.
The State Department announced the extra days of talks only hours before the expiration of the target date for their completion.
The June 30 deadline day 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.
"I will walk away from the negotiations if, in fact, it's a bad deal," Obama told reporters.
