Talks between Iran and the United States over Tehran’s rapidly advancing nuclear program are “in a very crucial” stage.

The UN nuclear watchdog should play a role in nuclear talks between Tehran and Washington, International Atomic Energy Agency chief Rafael Grossi said on Thursday, ahead of a second round of talks between the U.

But Iran’s foreign minister said Tehran planned to participate “calmly and coolly” in the negotiations. Both sides will meet in Rome on Saturday for a second round, Iran’s Foreign Ministry said.