Iran has expanded its uranium conversion facilities in Isfahan and reinforced its Natanz underground uranium enrichment plant, a US think tank said, amid growing concern over possible US military action.

Talk of a US attack has topped the international news agenda since a report in New Yorker magazine said this month that Washington was mulling the option of using tactical nuclear weapons to knock out Iran's subterranean nuclear sites.

Former Iranian President Akbar Hashemi Rafsanjani said Sunday that any US attack on Iran over its nuclear program would plunge the region into instability. 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 (ISIS) said in an e-mail with commercial satellite photos attached sent to news media that Iran has built a new tunnel entrance at Isfahan, where uranium is processed into a feed material for enrichment. Just two entry points existed in February, it said.

"This new entrance is indicative of a new underground facility or further expansion of the existing one," said ISIS, led by ex-UN arms inspector and nuclear expert David Albright.

ISIS also released four satellite images taken between 2002 and January 2006 it said showed Natanz's two subterranean cascade halls being buried by successive layers of earth, apparent concrete slabs and more earth and other materials. The roofs of the halls now appear to be eight meters underground, ISIS said.

The revelations came one week after Iran announced it had enriched uranium for use in power stations for the first time, stoking a diplomatic row over Western suspicions of a covert Iranian atomic bomb project. Iran says it seeks only nuclear energy for its economy.

President George W. Bush has dismissed reports of plans for a US military strike against Iran as "wild speculation" and said he remained focused on diplomacy to defuse the standoff. Despite Bush's denial, Iran's Rafsanjani said Teheran could not discount the possibility of a US military strike.

(China Daily April 17, 2006)