The International Atomic Energy Agency (IAEA) on Thursday chose Romanian diplomat Cornel Feruta as its acting director-general to replace Yukiya Amano, who died last week.
"In order to ensure the orderly and smooth functioning of the Agency, the Board of Governors has decided to designate Mr Cornel Feruta as acting Director General," the UN nuclear watchdog said in a statement released after a board meeting.
The race to succeed Amano on a permanent basis will be particularly keenly watched given heightened international tensions over Iran's nuclear activities.
The agency is currently confronted with the unravelling of the 2015 nuclear accord with Iran, which began when President Donald Trump unilaterally pulled the United States out of the agreement in May 2018.
The IAEA is tasked with monitoring Iran's nuclear activities to ensure they abide by the terms of the deal.
Another meeting of the agency's board of governors is expected next week to confirm the schedule for appointing a permanent director-general.
According to a source close to the agency, the procedure would normally take around a year but could be expedited so the new candidate is able to take office in January.
Feruta, 43, who worked as a journalist before entering Romania's diplomatic service in 1998, was one of Amano's closest collaborators and had been serving as the agency's chief coordinator.
He has been tipped as one of the likely candidates for director-general along with Rafael Grossi, Argentina's ambassador to the IAEA.
Amano had led the agency since December 2009 and died last week at the age of 72.
No details were released about the cause of death, but he had been ill for several months.