The United Nations nuclear watchdog's head said on Wednesday that he "could not agree" in talks with Iranian officials to resolve disputes over the country's atomic program a day after returning from Tehran.  

"We could not agree yesterday, despite my best efforts," Rafael Grossi, director general of the International Atomic Energy Agency (IAEA), told reporters on Wednesday.

One of the most pressing disputes is getting access to the workshop at the TESA Karaj complex two months after Iran promised to grant it. 

There is not much time for the atomic watchdog to gain access to reinstall cameras at a centrifuge-parts workshop in Iran, as the agency cannot guarantee that equipment is not being diverted to make atomic bombs, he said.

Tehran blames Israel for what it says was an attack that destroyed one of four IAEA cameras there. Iran later removed all the cameras, and the destroyed camera's footage is missing.

The IAEA has repeatedly said it has no sign that Iran has a secret weapons program, and Iran insists its aims are peaceful. But Grossi said he still does not know whether or not Karaj is operational five months after the apparent attack. 

The issue is a complicating factor ahead of indirect talks between the United States and Iran on reviving the 2015 nuclear deal with major powers that resumes in Vienna on Monday. 

(With input from agencies)