Iranian state television has said the country's military fired a missile to test air defenses over Natanz, a city that houses nuclear sites.
The announcement came after unconfirmed local reports on December 4 of a blast in the sky above the city, in central Iran, about 200 kilometers from the capital, Tehran.
"Iran's air-defense units fire missile to test [the] rapid-reaction force over Natanz city," read a bulletin on Press-TV, Iran's English-language international broadcaster.
Natanz hosts an underground center for centrifuges that enrich uranium, which is at the center of Western allegations of secret military nuclear activities.
"Such exercises are carried out in a completely secure environment...and there is no cause for concern," army spokesman Shahin Taqikhani told state TV, according to Reuters.
AFP quoted a spokesman as saying, "An hour ago, one of our missile systems in the region was tested to assess the state of readiness on the ground, and there is nothing to fear."
The army was responding after widespread concern from locals who witnessed the unexplained blast.
No drills or exercises had been announced prior to the incident.
"Local sources have reported hearing a large explosion in the Natanz sky," the ISNA news agency said earlier on December 4. "No official source has yet confirmed or denied the report."
The semiofficial Fars news agency quoted a reporter in a nearby city as saying an intense light had been seen and a blast rang out.
"No exact details are available about this," Fars quoted a local governor as saying, according to Reuters.
Later, Press-TV published a breaking story that said simply that "Iran’s air defense force" had confirmed the "test."
Iran blamed Israel for what it called an attack on Natanz when a power cutoff caused a blackout at the facility in April.
Multiple incidents at Iranian nuclear and scientific facilities and assassinations of leading nuclear scientists have been blamed by Iranian officials on Israel or the West.
A seventh round of international talks in Vienna aimed at reviving a 2015 nuclear deal between Iran and world powers including the United States ended on December 3 with talk of new setbacks.
Israel has threatened to take military action if diplomatic efforts to prevent Iran from acquiring a nuclear weapons capability fail.
Iran has consistently rejected accusations it is developing nuclear weapons and says its atomic activities are for civilian aims, despite findings by the International Atomic Energy Agency (IAEA) that Tehran previously obfuscated and deceived over its nuclear activities.
Secretary-General Rafael Grossi warned after a trip to Tehran last month that time was running out for the IAEA to gain access to reinstall cameras at a workshop in Iran that makes parts for advanced centrifuges, saying its inspectors would soon be unable to "guarantee" equipment there was not being diverted to a potential secret nuclear program.