Delegates wait for the start of the International Atomic Energy Agency (IAEA) board of governors meeting at the International Center, in Vienna,, Austria, Monday, June 2, 2014.
The head of the U.N. nuclear agency suggested Monday that a probe of suspected atomic arms work by Iran may stretch into next year - which would push Tehran's overall nuclear agreement with world powers long past the July 20 target date.
The International Atomic Energy Agency investigation is formally separate from six-power talks with Iran that are meant to build on a first step-accord struck late last year and focus on substantially trimming Tehran's nuclear program in exchange for full sanctions relief.
The U.S. and its western allies at the negotiating table insist that Iran and the IAEA must wrap up the investigation as part of the overall nuclear agreement that Iran and the powers want to finalize by July 20.
On Monday, IAEA chief Yukiya Amano told reporters he doesn't believe either side expects his agency to conclude its probe by then - raising new doubts about the deadline. He could not say if the investigation would finish by year's end.
Speaking to the 35-nation IAEA board, Amano said Iran is cooperating "substantively" with the probe, but it is too early to make an overall judgment.
After years of deadlock, Iran recently submitted documents to the IAEA for the first time, to back its claim that its tests with a special kind of detonator were meant only for civilian purposes.
Iran denies any interest in nuclear arms. But agency officials say they have other documentation indicating that those experiments were linked to research on setting off a nuclear charge.
The detonator suspicions are only a small part of a wide range of alleged nuclear weapons-related experiments that Amano - and the United States - want cleared up.
The nuclear talks resume June 16. Hopes for meeting the target date already dimmed after major disagreements at the negotiating round last month prevented the two sides from starting to draft a pact as hoped.
The talks can be extended by mutual agreement. But the U.S. and Iranian governments are under huge domestic pressure to show progress - from both Iranian hardliners and U.S. congressional critics.