The sprawling Parchin military site, located 30 kilometres east of Tehran, "is conducting normal military activities," foreign ministry spokesman Ramin Mehmanparast told reporters in a regular briefing.
"Declarations about the cleaning up of nuclear traces from this site -- and those who are technically savvy know you cannot remove traces of such activity from an area -- these declarations are propaganda," he said.
The head of the UN nuclear watchdog, Yukiya Amano, said early last week that satellite images suggested there were unspecified "ongoing" activities at the Parchin base. Western diplomats said they suspected Iran was removing evidence from the site.
The International Atomic Energy Agency has focused suspicions on Parchin since receiving intelligence, outlined in a November report, that Iran may have been testing normal explosives in a big metal cylinder there with the aim of researching implosion triggers for an eventual nuclear bomb.
Iran has twice this year refused requests by a visiting IAEA team to inspect Parchin. Although the IAEA inspected parts of Parchin two times in 2005, it says it did not see the area alleged to contain the explosives test cylinder.
Mehmanparast highlighted those 2005 visits and said Iran had accepted the "principle" of another visit, but that the IAEA should have been "more patient" in reaching agreement on the framework of such an inspection. Parchin will be one of the key issues in a new round of talks being prepared between Iran and world powers likely to take place in coming weeks.