Vienna:
The UN atomic agency said on Friday it has "major differences" with Iran and "major concerns" about its nuclear programme, after inspectors probing suspected weapons work returned from Tehran empty-handed.
"An intensive discussion was held on the structured approach to the clarification of all outstanding issues related to Iran's nuclear programme" during two recent visits, the agency said in a new report.
"No agreement was reached between Iran and the Agency, as major differences existed with respect to this approach," the International Atomic Energy Agency said.
"The agency continues to have serious concerns regarding possible military dimensions to Iran's nuclear programme."
It added that Iran had tripled production of 20-percent enriched uranium since its last assessment in November, with 696 centrifuges installed at its heavily bunkered Fordo site -- all of them older-generation, however.
Uranium further enriched to 90-percent purity could in theory be used in a nuclear bomb, although Iran denies intending to do so, saying its activities are peaceful.
A senior official familiar with the investigation said that during their two visits to Tehran in the past month -- no more trips are planned for now -- IAEA inspectors spoke only to "middle men."
"Iran wanted to constrain the process, and put us in a harness," the official said on condition of anonymity.
In particular, the IAEA said there was a "disappointing" refusal by Iran to allow the team access to the Parchin military site near Tehran, where a November IAEA report said scientists had conducted suspicious explosives tests.
That extensive report focused on a number of areas where the IAEA believes Iran carried out activities the agency said could only conceivably be aimed at developing nuclear weapons.
Iranian officials repeated their assertion during the recent visits that the report, which has prompted Western countries to ramp up sanctions and raised speculation of Israeli plans to carry out air strikes, was based on forgeries, the agency said.
"Iran's declaration dismissed the agency's concerns in relation to the aforementioned issues, largely on the grounds that Iran considered them to be based on unfounded allegations," the IAEA said.
"The director general urges Iran to work with the agency to reach agreement on a structured approach, based on agency verification practices, to resolve all outstanding issues," it added.
"In particular, the director general urges Iran to address the agency's serious concerns about possible military dimensions to Iran's nuclear programme, including, as a first step, by responding to the agency's questions related to Parchin... and by granting early access in this regard."
The senior official familiar with the investigation said Iran was now producing around 14 kilos of 20-percent enriched uranium per month, and that it now had around 105 kilos already enriched.
Iran has "placed in position" 2,088 empty centrifuge casings at Fordo, which Iran kept secret until September 2009, and all the piping had been installed, the report said.
Experts say that once up and running, Fordo, under a mountain near the holy city of Qom, could slash the time needed to convert Iran's stockpile of low-enriched uranium to 90 percent -- if it decided to do so.
Diplomats to the Vienna-based IAEA are discussing what action the 35-member IAEA board will take at its next regular meeting from March 5.
In theory it could pass a resolution condemning Iran and reporting the Islamic republic to the UN Security Council, which has already passed four rounds of sanctions.
This though depends on Russia and China, which have so far been more lenient on Iran that their Western counterparts.