Activities included computer modelling of a nuclear warhead Iran was under fresh scrutiny Wednesday after the UN atomic watchdog released reams of what it called "credible" intelligence suggesting Tehran had worked on developing nuclear weapons. With Washington threatening to increase international pressure on Iran and Israel's president stoking speculation of a pre-emptive strike, the International Atomic Energy Agency report was set to stoke Middle East tensions.
The Vienna-based watchdog said it had "serious concerns" based on "credible" information indicating that the Islamic republic "has carried out activities relevant to the development of a nuclear explosive device."
Although some of the areas listed in 12 dense pages of intelligence "have civilian as well as military applications," the keenly-awaited report said that "others are specific to nuclear weapons."
Activities included computer modelling of a nuclear warhead, testing explosives in a large chamber at the Parchin military base near Tehran and studying how to arm a Shahab 3 medium-range missile with an atomic warhead.
"The report details Iranian activities that can only be explained if the purpose was to develop a nuclear bomb," one Western diplomat in Vienna said.
Iran, which says its nuclear programme is peaceful, immediately rejected the report, which was based on input from more than 10 foreign intelligence agencies plus the IAEA's own information, calling it groundless.
Tehran's envoy to the Vienna-based agency, Ali Asghar Soltanieh, told the Iranian news agency Fars it was "a repetition of old claims which were proven baseless by Iran in a precise 117-page response."
The United States said the report showed that Iran had lied and said it would seek to ratchet up pressure and may seek new sanctions.
US Senator John Kerry, head of the Senate Foreign Relations Committee, said the report made it clear that Iran "has not been truthful" and that the international community had to "increase pressure" on Tehran.
"Iran's leaders know what they need to do, the question is how we ensure they start doing it," Kerry said.
But analysts said that the report was not enough of a "smoking gun" for the United States and its allies to be able to convince fellow UN Security Council permanent members Russia and China of the need for more sanctions.
"This isn't new blockbuster information," nonproliferation analyst Peter Crail from the Washington-based Arms Control Association told AFP. "It does not suggest that they are on the verge of making a nuclear weapon."
He said however that the US could make a "very strong case" for strengthening the existing sanctions, since they give countries latitude to take additional steps of their own that could hurt Iran's uranium enrichment activities.
Russia and China are likely to block any attempt by the IAEA board to report Iran to the UN Security Council when the board meets next Thursday and Friday in Vienna, experts said.
Moscow on Tuesday even went so far as to express anger over the publication of the report, saying it risked damaging the chance of a renewal of talks, with the foreign ministry saying it was "gravely disappointed and bewildered."
In Israel, Foreign Minister Avigdor Lieberman said before the IAEA report only crippling sanctions against Iran's central bank and its oil and gas industries would force Tehran to halt its nuclear drive.
"If, after the IAEA report comes out, the United States does not lead an initiative of crippling sanctions against Iran, this will mean that the United States and the West have accepted a nuclear Iran," he said in Maariv newspaper.
Israeli President Shimon Peres had said on Sunday that a strike against Iran was becoming more likely, in one of the starkest warnings by the Jewish state to Tehran in recent times