IAEA chief Yukiya Amano will travel to Tehran on Sunday to meet with senior Iranian leaders Monday, the international nuclear watchdog group announced Friday amid rumors of a breakthrough in talks between world powers and Iran.

According to a brief published on the IAEA website, the aim of Amano’s visit to Iran is “strengthening dialogue and cooperation” between the Islamic Republic and the nuclear agency.

It was not immediately clear with whom Amano would speak during his visit.

Tehran has prevented IAEA inspectors from visiting sites suspected of producing material for a nuclear weapon.

On his arrival in Geneva earlier on Friday, US Secretary of State John Kerry warned of significant differences between Iran and six world powers trying to fashion a nuclear agreement, as he and three European foreign ministers added their weight to try to narrow the gap.

Officials had expressed optimism about progress achieved in Thursday’s full day of talks. But comments from Kerry and his counterparts from Britain, France, and Germany, after they arrived in Geneva, clearly indicated that some obstacles remain in the way of any agreement offering sanctions reductions for nuclear concessions.

Kerry arrived from Tel Aviv after talks with Israeli Prime Minister Benjamin Netanyahu where he tried to defuse Israeli concerns about the Geneva talks. Israel is strongly critical of any deal that even slightly lifts sanctions unless Iran is totally stripped of technology that can make nuclear arms.

The talks primarily focus on the size and output of Iran’s enrichment program, which can create both reactor fuel and weapons-grade material suitable for a nuclear bomb. Iran insists it is pursuing only nuclear energy, medical treatments and research, but the United States and its allies fear that Iran could turn this material into the fissile core of nuclear warheads.