Iran's nuclear chief was blocked from attending an annual conference on Monday at the headquarters of the UN's nuclear agency in Vienna due to opposition from the United States, Iranian state television said.
"Mohammad Eslami and his delegation took a regular flight to Vienna on Saturday, but were blocked on the way because of obstructions by the United States," the state broadcaster reported, saying he had returned to the capital Tehran.
He was due to attend the annual general conference of the International Atomic Energy Agency (IAEA), the UN's nuclear watchdog, which runs until Friday in Austria.
He attended last year's conference and delivered a speech there on behalf of Iran, a member state of the IAEA.
Tehran summoned Austria's charge d'affaires in response to the decision to bar Eslami.
"The Austrian government's refusal to issue visas to the delegation of the Islamic Republic of Iran is a completely unjustified decision," foreign ministry spokesman Esmail Baghaei said at a press conference in Tehran attended by AFP.
"It is clear to us that this incident occurred under American pressure, but that does not absolve the Austrian government of responsibility."
A diplomatic source in Vienna, speaking on condition of anonymity, confirmed that Eslami was refused entry to Austria due to US pressure.
The United States and Israel launched a war against Iran on February 28, arguing that its nuclear programme posed a threat.
For decades, Western powers have suspected the Islamic republic of seeking to acquire nuclear weapons, a claim that Tehran categorically denies.