By Lesley Wroughton
GENEVA (Reuters) - U.S. Secretary of State John Kerry met his Iranian counterpart Mohammad Javad Zarif on Saturday in a bid to overcome the remaining obstacles to a final nuclear agreement, a month ahead of a deadline for a deal between Tehran and world powers.
The meeting in Geneva is the first substantive talks since Iran and the six world powers - Britain, France, the United States, Russia, China and Germany - struck an interim deal on April 2.
Among the issues still to be resolved is the push by the world powers for international access to Iran's military sites and its team of atomic experts. For its part, Tehran wants sanctions to be rescinded immediately after a deal is reached.
A senior U.S. State Department official said there had been substantial progress in talks in Vienna in recent weeks on drafting a political agreement and three technical annexes on curbing Tehran's nuclear program.
The United States has said it will not extend the talks beyond the June 30 deadline. "We really do believe we can get it done by (June) 30th and we're not contemplating an extension. We just aren't," the official told reporters traveling with Kerry to Geneva.
But France, which has demanded more stringent restrictions on the Iranians, has indicated talks are likely to slip into July. Iran's senior nuclear negotiator Abbas Araqchi also warned that the deadline might need to be extended.
"We are on a good track right now to make progress and we absolutely believe it is possible we can get this done by June 30," the senior State Department official said, adding that Kerry's schedule for June had been cleared to focus on the Iran talks.
"A lot of the decisions (left) are at the political level. You will see more involvement at (Kerry's) level for that reason," the official said, adding that the talks would likely occur in Vienna.
Zarif, when asked at the start of the talks on Saturday whether the deadline would be met, replied: "We will try."
One Western diplomat said inspections of military sites by U.N. nuclear watchdog the International Atomic Energy Agency (IAEA) and access to Iran's scientists were critical to monitoring and verifying whether Iran was pursuing a clandestine nuclear weapons program.
"If the IAEA can't have access to (the scientists) or the military sites then its a problem," the Western diplomat said. "The IAEA needs sufficient access quickly to those sites to ensure things don't just disappear."
The State Department official took a similar view, saying without access "we're not going to sign" a deal.
Iran denies any ambition to develop a nuclear weapon and says its program is purely peaceful. Its supreme leader, Ayatollah Ali Khamenei, has said Tehran will not accept "unreasonable demands" by world powers.
"The issue of interviews with nuclear scientists is generally off the table as well as the inspection of military sites," Araqchi told reporters as he arrived for the talks with Kerry. "How additional protocol would be implemented is still a matter of disagreement that we are still talking about."
Iran's demand that sanctions be rescinded immediately after a deal is also among the issues holding up a settlement as the powers' have said they can only be lifted in phases depending on Tehran's compliance with the terms.
Tehran-based analyst Saeed Laylaz said he expected a deal to be finalised despite resistance from opponents in Iran and the United States.
"Neither America nor Iran have a choice but to reach a deal," he told Reuters. "Failure to reach a deal will fuel tension in the region."
Mark Fitzpatrick, a former State Department official now at the International Institute for Strategic Studies, said an agreement was likely some time in July.
"The most difficult compromises have already been made," he said. "But the Iranians could overplay their hand on the incorrect assumption that Obama needs a deal more than they do."
(Additional reporting by Parisa Hafezi in Ankara, John Irish in Paris and Lou Charbonneau at the United Nations Editing by Pravin Char)