A UN inquiry into intelligence allegations of secret atom bomb research in Iran has reached a standstill because of Iranian failure to cooperate, an International Atomic Energy Agency (IAEA) report said on Monday.
Iran said the IAEA bore the blame for lack of progress. A senior Iranian official, who asked not to be named, said it must change its approach and work in a "legal and logical" manner.
A confidential IAEA report said Iran had raised the number of centrifuges enriching uranium to 3,820, compared with 3,300 in May, with over 2,000 more being installed.
"We have arrived at a gridlock," said a senior UN official familiar with the latest report, which urged Iran to take the intelligence allegations seriously to defuse suspicions its nuclear work is not entirely peaceful.
But Iran seemed some way from refining enough uranium to build a nuclear weapon, if it chose, the report indicated.
Iran had stockpiled 480 kg (1,050 pounds) of low-enriched uranium so far. It would need 15,000 kg (33,000) to convert into high-enriched uranium for fuelling an atom bomb, said UN officials who spoke on condition of anonymity.
"That would be a significant quantity, one unit of HEU, and would take on the order of two years," said one official.
On the day the report emerged, Iran announced air defense exercises in half of the Islamic Republic's 30 provinces.
"(Air defense commander Brigadier General Ahmad Mighani) emphasized that the enemies would receive a serious response for any aggression and we would surprise them and make them regretful," the ISNA agency in Tehran reported.
Washington says it wants a diplomatic solution to the nuclear standoff, but has not ruled out military action if that fails. Iran, the world's fourth-largest oil exporter, says its nuclear program is a peaceful drive to generate electricity.
ElBaradei calls for 'full disclosure'
In its last report in May, the IAEA said Iran appeared to be withholding information needed to explain intelligence that it had linked projects to process uranium, test high explosives and modify a missile cone in a way suitable for a nuclear warhead.
IAEA Director Mohamed ElBaradei called on Iran then for "full disclosure" - namely, going beyond flat denials without providing access to sites, documentation or relevant officials for interviews to substantiate their stance.
Monday's report said Iran had done nothing to that end.
"Regrettably the agency has not been able to make any substantial progress on the alleged (weaponization) studies and other associated key remaining issues which remain of serious concern," the report said.
It said IAEA investigators had stressed to Iran that the intelligence documentation was detailed and
consistent enough "that it needs to be taken seriously (by Iran), particularly in light of the fact that, as acknowledged by Iran, some of the information contained in it was factually accurate," it said.
"Unless Iran provides such transparency, and implements the (IAEA's) Additional Protocol (allowing wider-ranging, snap UN inspections), the agency will not be able to provide credible assurances about the absence of undeclared nuclear material and activities in Iran," said the report.
It also reaffirmed that in continued defiance of the UN Security Council, Iran had not suspended enrichment-related work, continued to expand centrifuge capacity and was testing a advanced machines, able to refine uranium 2-3 times faster.