The head of the U.N. nuclear agency says he expects Iran to sign a deal with the International Atomic Energy Tangency “quite soon.”

But IAEA chief Yukio Amano told reporters Tuesday in Vienna that there were still some differences that needed to be sorted out. Amano has just returned from Tehran, where he held talks with Iran's top nuclear negotiator, Saeed Jalili, and the Iranian nuclear energy organization chief, Fereydoon Abbasi-Davani.

It was Amano's first trip to Iran since taking office at the U.N. nuclear agency in 2009. He was expected to discuss Iran's running dispute with the U.N. over access to Iranian facilities that are suspected of being used for a covert nuclear weapons program.

Iran has rejected repeated IAEA requests to inspect its Parchin military complex in response to Western allegations of atomic weapons research at the site. Tehran says the complex houses only conventional weapons and insists the Iranian nuclear program is peaceful.

After the talks, Jalili said he had a good discussion with Amano about how to cooperate on global nuclear disarmament, stopping the spread of nuclear weapons and supporting the rights of IAEA member states.

Jalili arrived in Baghdad, Iraq, late Monday ahead of nuclear talks with world powers on Wednesday.

The world powers include the five permanent members of the U.N. Security Council plus Germany – a group that has been trying to assess the possible military capability of Iran's nuclear sites.

Israel sees a nuclear-armed Iran as a threat to its existence and refuses to rule out military action against the Iranian nuclear program.

Israeli Prime Minister Benjamin Netanyahu called Iran a threat to the entire world Monday and urged world powers not to make concessions to Iran at the talks.

The United States also has refused to rule out a strike on Iran to prevent it from obtaining nuclear weapons.