A UN nuclear inspector was killed and another injured in a car accident in central Iran on Tuesday, the country's Atomic Energy Organisation said.
It named the deceased inspector as Seo Ok-seok, a South Korean member of an inspection team which the UN's International Atomic Energy Organisation (IAEA) maintains in Iran.
Seo was on a mission with an IAEA colleague near the Khondab complex in the province of Markazi, it added in a statement, without naming the other inspector injured in the accident at around noon (0730 GMT).
"One of the two experts was injured, while Seo Ok-seok from South Korea died of severe injuries," read the statement, carried by the official IRNA news agency.
It added the car had overturned after veering off the road.
Two other news agencies, ISNA and Fars, said the second inspector was a Slovak national, who has been hospitalised. They did not provide further details.
In Seoul, a foreign ministry spokeswoman confirmed the details of the death but said an IAEA official from Slovenia and an Iranian driver were hospitalised with injuries.
Iran is building a heavy water research reactor on the outskirts of the village of Khondab, 186 kilometres (116 miles) west of Tehran.
Iran's disputed nuclear programme is under the supervision of the IAEA, which has managed to keep its presence in the country despite disputes with the West over Tehran's atomic work.
The crash on Tuesday came ahead of a meeting between Iran and the UN nuclear watchdog at its headquarters in Vienna on May 13 and 14 aimed at clearing up questions over Tehran's atomic work.
The talks are expected to explore technical issues linked to an expansion of inspections of Tehran's nuclear activities, which the United States and its European allies suspect mask a drive to acquire a nuclear weapons capability.
Iran's leaders insist their work is purely peaceful in nature.
The last such talks between the Islamic republic and IAEA, in early February, ended in impasse when a team visiting Tehran said it had been repeatedly refused permission to inspect Parchin military site, also near the capital.
Iran says it is under no obligation to allow access to Parchin because the site is not a declared nuclear activities facility.
The UN Security Council has imposed four rounds of sanctions on Iran because of suspicions over its nuclear programme.