The head of the UN nuclear agency flew to Tehran on a delicate mission that - if successful - could finally lift the veil on whether Iran is seeking atomic arms while strengthening the Islamic Republic's negotiating hand in crucial nuclear talks with six world powers later in the week.
The trip by International Atomic Energy Agency chief Yukiya Amano is focused on getting agreement from Iran to terms that will allow the agency to resume probing whether Tehran secretly worked on nuclear arms.
Even if that happens, Western diplomats have expressed scepticism that Iran will honour a deal. But with both Iran and the IAEA reporting progress in a previous round last week, anticipation was high as Mr Amano prepared to board his flight to Tehran.
While expressing some optimism, Mr Amano said he could not predict whether he would clinch a deal that would allow his agency to renew its long-stalled probe.
“Nothing is certain in life, in diplomacy,” he told reporters at Vienna's airport. “But there has been good progress.
“I really think this is the right time to reach agreement.”
The one-day trip is significant both for what it can achieve in terms of probing Iran's secretive nuclear programme and as a mood-setter for talks in Baghdad between Iran and the United States, Russia, China, Britain, France and Germany.
The latter six nations are in the forefront of trying to persuade Tehran to curb its nuclear programme and ease concerns it wants to use it to make nuclear weapons.