Yukiya Amano told reporters in Paris following a one-day trip to Tehran an apparent breakthrough was reached in negotiations with the Islamic republic concerning potential military applications for its nuclear program, The New York Times reported Tuesday.
"There remain differences," he said but added an "important development" was reached on the IAEA's push for a "structured agreement" to determine how inspectors would conduct an investigation.
"The decision was made to conclude and sign the agreement," Amano said.
His visit to Tehran Monday was his first since his appointment to the U.N. agency in 2009.
The trip was announced Friday as part of what diplomats in Vienna called an effort centered on persuading Iran to allow inspections of a site the IAEA suspects was used for secret tests of triggering mechanisms for a nuclear weapon.
The timing of Amano's announcement of progress comes just one day ahead of negotiations in Baghdad on Iran's enrichment of uranium.
Iran has said the program is for peaceful purposes but Western powers suspect the goal is development of a nuclear weapon.