TEHRAN - A fruitless visit to Iran by UN nuclear inspectors sparked anger and raised tensions on Wednesday, with Russia warning of “catastrophic” consequences if it leads to a military attack on its ally.

France said Iran’s refusal to allow the inspectors to see a key military site used for suspected atomic weapons research was a “missed opportunity” that could undermine chances of reviving wider talks between Tehran and world powers. Iran’s supreme leader, Ayatollah Ali Khamenei, was defiant, however.

He made no mention at all of the failed bid by the International Atomic Energy Agency inspectors. Instead he reiterated the assertion that “the Iranian nation has never been seeking an atomic weapon and never will be.” Possessing a nuclear bomb, he said, “constitutes a major sin,” he told a group of nuclear scientists.

Khamenei added: “Pressure, sanctions, threats and assassinations will not bear any fruit and Iran will continue its path of (nuclear) scientific development.”

The IAEA said it had gone into the two-day visit to Tehran — and a previous, inconclusive one last month — in a “constructive spirit,” but that no agreement had been reached on efforts to elucidate Iran’s nuclear activities.

Despite requests, “we could not get access” to Iran’s military site in Parchin where suspected nuclear warhead design experiments were conducted, the leader of the IAEA team, chief UN inspector Herman Nackaerts, said on his return to Vienna. IAEA chief Yukiya Amano said the Iranian’s refusal to allow the Parchin inspection was “disappointing.”

The IAEA said that “at this point in time” there was no agreement with Iran on holding further talks. A Western diplomat in Vienna said that Iran’s decision on Parchin showed why the international community “lacks confidence in the nature of its nuclear programme.”

“This latest snub, along with its decision to begin enrichment at Qom, underscore Iran’s defiance of the international community and multiple Security Council resolutions,” said the diplomat.

The IAEA trip was seen as having an impact on the mooted resumption of talks between Iran and the P5+1 powers — Britain, China, France, Russia and the United States, plus Germany — which broke down 13 months ago. France said Iran’s “refusal to cooperate” was “another missed opportunity” that added to a standoff already aggravated by the Islamic republic’s recent boasts of nuclear progress.

“We cannot but consider all of this contrary to the intentions” declared by Iran to resume negotiations with the P5+1, said a spokesman. Oliver Thraenert, an analyst with the German Institute for International and Security Affairs, said the IAEA visit “shows clearly that Iran is not in the mood for substantial compromise.” “The chances now of a return to negotiations between Iran and the P5+1 are not very high. It leaves matters in a deadlock.” Already talk of possible military action against Iran by Israel, with or without US help, had been giving urgency to diplomatic attempts to lower tensions.

Russia, which along with China has been giving Iran diplomatic cover, warned against that prospect. “The scenario of military action against Iran would be catastrophic for the region and possibly the whole system of international relations,” said Deputy Foreign Minister Gennady Gatilov. Russia on Wednesday said it could not rule out that the United States would use the US Manas airbase in ex-Soviet Kyrgyzstan for an eventual strike on Iran over its contested nuclear programme. “It cannot be excluded that this site could be used in a potential conflict with Iran,” foreign ministry spokesman Alexander Lukashevich told reporters. “We hope that such an apocalyptic scenario will not be realised.”

Kyrgyzstan President Almazbek Atambayev in December said it was “very dangerous” for the state to host the US Manas military airbase and has threatened the Americans with eviction when the current lease expires in 2014. The US base, which is located at the airport in the capital Bishkek, is currently used as a key coalition hub for operations in nearby Afghanistan.

Lukashevich said using the airbase as a launch-pad to strike Iran would require “changes or rather violations” to the lease agreement between Washington and Bishkek.

“The statements from Washington which do not rule out a military solution to the Iranian nuclear crisis have caused serious worries in the Central Asian region,” he said.

“The worries are shared not just by Kyrgyzstan — where a debate has erupted about the risk of a retaliatory strike from Iran — but other Central Asian countries,” he added.

The United States and its chief regional ally Israel have never ruled out a military strike against Iran over its controversial nuclear programme but Russia has always insisted the standoff can only be solved through diplomacy.

Russia also has a military base in Kyrgyzstan and has long vied with Washington for influence in the country as Moscow seeks to preserve its ascendancy in the ex-Soviet region.