The head of the United Nations nuclear watchdog agency says Iran has agreed in principle to an international probe of its alleged nuclear weapons projects.
However, no deal on such an investigation has yet been finalized.
International Atomic Energy Agency (IAEA) chief Yukiya Amano told reporters in Vienna that a deal between Tehran and the IAEA would be signed soon but that some minor differences still need to be resolved.
He said he expected that access to the Parchin military site near Tehran, where the IAEA wants to look for signs of possible nuclear warhead tests, would be part of the agreement.
Some experts believe Iran conducted explosive tests in a specially built pressure chamber at Parchin in 2003 as part of a covert nuclear weapons program. Iran denies any effort to make a nuclear weapon.
Amano was speaking after returning from a two-day trip to Tehran to assess Iran's readiness to grant inspectors improved access to suspect Iranian sites.
In Washington, U.S. State Department spokeswoman Victoria Nuland welcomed the IAEA's announcement, but added that the United States was waiting to see what emerges.
"Obviously, the announcement of the deal is one thing, but the implementation is what we're going to be looking for -- for Iran to truly follow through and provide the access to all of the locations, the documents, and the personnel that the IAEA requires in order to determine whether Iran's program is exclusively for peaceful purposes," Nuland said.
Amano's announcement also came on the eve of the next round of international talks on the Iranian nuclear program in the Iraqi capital, Baghdad. That gathering is scheduled to bring Iran together with the representatives of six world powers -- Britain, China, France, Germany, Russia, and the United States.
Reports say Tehran may call for the lifting of Western sanctions against the Islamic republic in exchange for letting international inspectors visit suspect Iranian sites.
The last round of such talks -- in April in Istanbul -- failed to result in a breakthrough.
Iran's chief nuclear negotiator Said Jalili said he hopes for the "beginning of a new cooperation" between Iran and the international community.
"We had an agreement in Istanbul. That is the basis for the beginning of a new cooperation," he said. "We hope that the talks in Baghdad will be a kind of dialogue that will give shape to such cooperation."
Israeli Prime Minister Benjamin Netanyahu, meanwhile, has repeated allegations that Iran is seeking atomic weapons to destroy the Jewish state. He called on Western powers to make no concessions on Iran's nuclear program during the Baghdad meeting.
"Iran wants to destroy Israel. It is developing nuclear weapons to carry out this goal. Iran threatens Israel. It threatens the peace of the entire world," Netanyahu said. "Given these evil intentions, the leading powers in the world must show force and clarity and not weakness. They shouldn't make concessions to Iran.
"They should present sharp and unequivocal demands: To stop all enrichment of nuclear material in Iran, to take out of Iran nuclear material enriched until now, and to dismantle the underground nuclear facility near the city of Qom. Only in this way can it be possible to ensure Iran won't have a nuclear bomb. This is Israel's position. It hasn't changed and it won't."
Israel and its ally the United States have declined to rule out military action to try to hobble the Iranian nuclear program.
The Islamic republic is currently under four rounds of United Nations sanctions over its refusal to halt uranium processing work that could be directed toward development of a nuclear warhead.
The United States and the European Union have also imposed their own sanctions, including measures targeting Iran's oil sector and central bank, which are responsible for bringing in much of Iran's export revenue.
With reporting by Reuters, dpa, AFP, and AP