Iran is continuing to stall on UN investigation into its disputed nuclear programme, refusing to provide access to documentation, individuals or sites which could reveal the true nature of its activities, the UN atomic watchdog said Monday.
  
Furthermore, the Islamic republic is defying international demands to suspend uranium enrichment, a process that can be used to make the fissile material for an atomic bomb, the International Atomic Energy Agency said.
  
The United States warned Iran could now face possible new sanctions in the wake of the IAEA's findings.
  
The agency complained that it was making little headway in its investigation into allegations that Tehran had, in the past, been involved in studies to make a nuclear warhead.
  
The IAEA "regrettably has not been able to make any substantive progress on the alleged studies and other associated key remaining issues which remain of serious concern," said the restricted report, a copy of which was obtained by AFP.
  
The report, circulated to members of the IAEA's board of governors on Monday, was scheduled to be discussed at a board meeting next week.
  
"On this particular issue, we've arrived at a gridlock," a senior official close to the IAEA said, speaking on condition of anonymity.
  
The so-called "alleged studies" suggest Iran may have been trying to develop a nuclear warhead, convert uranium and test high explosives and a missile re-entry vehicle.
  
The information collected by IAEA from a wide number of sources was "of such a quality that Iran has to take it seriously" and had to provide a "substantive response," a UN official said.
  
"These studies point to real people, real organisation," the official said.
  
But Iran has so far done little to disprove the allegations, merely dismissing the evidence as "forged" and "fabricated".
  
In order for progress to be made, Iran "needs to provide the agency with substantive information to support its statements and provide access to relevant documentation and individuals in this regard," the IAEA said.
  
Unless Iran provided "such transparency ... the agency will not be able to provide credible assurance about the absence of undeclared nuclear material and activities in Iran."
  
Furthermore, "contrary to the decisions of the (UN) Security Council," Iran had still not suspended its uranium enrichment activities, the IAEA complained.
  
In fact, Iran had installed additional cascades of uranium-enriching centrifuges, bringing the number up and running to close to 4,000, and was testing more advanced centrifuges as well.
  
So far, Iran's enrichment plant in Natanz has produced a total of 480 kilogrammes (1,058 pounds) of low-enriched uranium or LEU, it said.
  
It would need 1,700 kilogrammes to convert into high-enriched uranium (HEU) for use in an atom bomb, a UN official said.
  
"That would be a significant quantity, one unit of HEU, and would take of the order of a couple of years, two years," a senior official said.
  
In Washington, the White House warned that the stalemate in the IAEA's investigation could lead to further sanctions against Iran.
  
"We urge Iran to suspend its uranium enrichment and reprocessing activities or face further implementation of the existing United Nations Security Council sanctions and the possibility of new sanctions," said spokesman Gordon Johndroe.
  
His comments echoed remarks made by IAEA Director General Mohamed ElBaradei in the summary of the report, who urged Iran "to implement all measures required to build confidence in the exclusively peaceful nature of its nuclear programme at the earliest possible date."
  
Iran, which insists that its nuclear programme is geared solely towards energy generation, is under three sets of UN sanctions over its refusal to freeze enrichment.
  
The US ambassador to the IAEA, Gregory Schulte, said Iran was continuing "to rebuff the IAEA across the board, whether by stonewalling its investigation of past weaponisation activities, refusing to implement the Additional Protocol (which allows more intrusive inspections of nuclear facilities) or refusing to provide new information on new nuclear facilities."
  
Iran's refusal to address outstanding questions "is particularly troubling as it is continuing to develop -- in violation of four Security Council resolutions -- the ability to produce fissile material that could be weaponised into a nuclear bomb," Schulte said.