VIENNA -- Iran has expanded uranium conversion facilities in Isfahan, and has reinforced an underground uranium enrichment plant, a US think tank said. The report arose amid growing concern over possible US military action.
Talk of a US attack has been a subject of news speculation since a report in the New Yorker said this month that Washington was considering tactical nuclear weapons to knock out Iran's nuclear sites.
The former Iranian president, Akbar Hashemi Rafsanjani, said yesterday that any US attack would increase instability.
The UN secretary-general, Kofi Annan also warned that US military intervention in Iran was not the best solution to resolve the nuclear standoff.
The Institute for Science and International Security said in an e-mail message sent to news media that Iran has built a new tunnel entrance at a uranium processing plant in Isfahan.
''This new entrance is indicative of a new underground facility or further expansion of the existing one," said the report by the Institute for Science and International Security, led by a former UN arms inspector, David Albright.
The Institute for Science and International Security also released four satellite images taken from 2002 to January 2006, which, it said, showed two subterranean cascade halls in Natanz, central Iran, being buried by earth, apparent concrete slabs, and more earth and other materials.
The roofs of the halls now appear to be 26 feet underground, the Institute for Science and International Security said.
The reports surfaced a week after Iran announced that it had enriched uranium for use in power stations for the first time. The announcement stoked a diplomatic rift over Western suspicions of a covert Iranian bomb project. Iran says it seeks nuclear power.
The UN Security Council has urged Iran to stop enrichment work and asked Mohamed ElBaradei, head of the International Atomic Energy Agency, to report on Tehran's reply on April 28.
Iran stood its ground when ElBaradei visited last week.
President George W. Bush has dismissed reports of plans for a military strike against Iran as ''wild speculation." He has said he remained focused on diplomacy to defuse the standoff.
But analysts said Iran was not taking any chances.
''Iran is taking extraordinary precautions to try to protect its nuclear assets. But the growing talk of eliminating Iran's nuclear programme from the air is pretty glib," Albright said in a telephone interview.
Despite Bush's denial, Iran's Rafsanjani said Tehran could not discount the possibility of a US military strike.
''Harm will not only engulf the Islamic Republic of Iran, but the region and everybody," the influential Iranian leader said while on a visit to Syria.
Iran's foreign minister, Manouchehr Mottaki, said that Tehran was still seeking a diplomatic solution, but that ''America should be aware it is not in a position to create another crisis in the region," apparently an allusion to Iraq.
Annan was quoted as telling ABC, the Spanish daily, that the situation was ''too heated" and that further aggravation would be a setback. ''I still think the best solution is a negotiated one, and I don't see what would be solved by a military operation," he was quoted as saying. ''I hope the will to negotiate prevails and that the military option proves to be only speculation."
Also yesterday, an Iranian group said 200 people had signed up to carry out ''martyrdom missions" against US and British interests if Iran was attacked.