Iran on Monday gave Mongolia's president a tour of its main uranium enrichment plant, the first time that it has opened the site to a foreign leader.
The visit by President Tsakhia Elbegdorj follows a summit of emerging nations in Tehran that Iranian officials said would showcase the failure of Western sanctions to isolate Iran diplomatically.
State TV showed Elbegdorj inspecting centrifuges used to enrich uranium at the facility in the central Iranian town of Natanz.
The West says Iran's nuclear program aims at developing weapons technology, but Iran says it is for peaceful purposes such as power generation and cancer treatment.
The broadcast said the Mongolian leader was able to visit whatever he wanted in the plant.
It suggested that Elbegdorj endorsed the Iranian claim.
"This site is a unique place. Maybe in other countries it is not possible to visit such a sensitive place," he was quoted as saying.
"I found out how the enriched uranium is being used for peaceful energy."
Inspectors of the UN nuclear agency visit the site regularly, and Iran has in the past allowed foreign diplomats and reporters to enter it as well.
Mongolia is one of the 120 members of the Nonaligned Movement of emerging nations, which last week held its summit in Tehran.
Iran said during the meeting that it would open its nuclear sites to participating delegates.