Iranian Foreign Minister Mohammad Javad Zarif will meet US Secretary of State John Kerry at the opening of a UN conference on the global anti-nuclear weapons treaty on Monday, as they try to make progress in talks on a long-term atomic deal.
Iran's top diplomat will be the first state party to the 1970 nuclear Non-Proliferation Treaty to address its 190 signatories at the United Nations headquarters in New York on behalf of 118 non-aligned nations that have signed the NPT, the world's benchmark disarmament pact.
Zarif and Kerry will meet on the sidelines to discuss negotiations on a landmark nuclear deal with the United States and five other global powers as they try to secure a final agreement with Iran by a June 30 deadline.
In a tentative deal reached on April 2 in Lausanne, Switzerland, between Iran and the six powers, Tehran, which denies seeking nuclear weapons, agreed to curb sensitive nuclear work for at least a decade in exchange for ending sanctions that have crippled its economy.
Diplomats need to iron out details about the timing of sanctions relief, the future of Iran's atomic research and development program, the exact nature of the IAEA's monitoring regime and what kind of uranium stockpiles Tehran will be allowed to keep under any final accord.
Sanctions are proving to be one of the biggest hurdles at the moment.
Iran's Supreme Leader Ayatollah Ali Khamenei has said all sanctions, including the most severe restrictions on its energy and financial sectors, should be lifted the moment a deal is signed. Western officials say that this is not what Tehran agreed to in Lausanne.
At that meeting, Zarif and European Union foreign policy chief Federica Mogherini read a joint statement that said the implementation of sanctions would be halted "simultaneously with the IAEA-verified implementation by Iran of its key nuclear commitments."
Western officials say that means sanctions will be lifted only after the IAEA verifies compliance.
A senior Iranian negotiator said last week that the latest round of nuclear talks in Vienna between Iran and the six powers made good progress.
US Republican senators have pledged to try to toughen a bill giving Congress the power to review a nuclear agreement with Iran, a move that could further complicate the talks.
During this month's NPT meeting, Austria is leading an initiative to ban nuclear weapons due to the immense humanitarian suffering they cause. Over 70 countries are backing it.
Israel, which opposes the nuclear deal with Iran, will be attending the conference as an observer for the first time since 1995 as it eyes closer ties with Arabs, who also fear Tehran's nuclear ambitions.
Israel is widely believed to have the Middle East's only nuclear arsenal. Like nuclear-armed India and Pakistan, Israel is not a signatory to the NPT. North Korea, which signed but later withdrew from the NPT, has tested nuclear devices.