Talks with Iran aimed at ending a long standoff on explaining the origin of uranium particles found at apparently old but undeclared sites are at "a very difficult juncture", UN nuclear watchdog chief Rafael Grossi said on Wednesday.
Grossi and Iran agreed in March on a three-month plan to get to the bottom of the issue, which has been a source of tension between Iran and Western powers even during wider negotiations aimed at bringing Tehran and Washington back into full compliance with the 2015 Iran nuclear deal.
