THE UN’S nuclear watchdog has reported that Iran has managed to produce a tonne of low-enriched uranium, which it says is enough to build a nuclear weapon.

International Atomic Energy Agency (IAEA) officials cautioned that there remained many obstacles to the production of a bomb, and yesterday’s report said Iran appeared to have slowed down the rate at which it is expanding its uranium enrichment capacity. But the report is likely to raise the already high tensions surrounding Iran’s nuclear programme.

One US analyst said that the one-tonne milestone meant Iran had reached “breakout capacity” – the theoretical ability to produce the 20-25kg of highly enriched uranium needed for one warhead.

Others were more cautious, but said there was plenty more matters in the report to raise the level of international concern.

The IAEA said that Iran had put a roof on a heavy water nuclear reactor being built near the town of Arak, and is preventing the agency from carrying out inspections, meaning they no longer had any way of seeing what was being done inside. Iran is also refusing to tell the IAEA where it is manufacturing the centrifuges used to enrich uranium, so the agency cannot confirm how many are being produced.

In a separate report released yesterday, the IAEA said traces of uranium taken from the site of an alleged nuclear reactor in Syria were man-made, and rejected the Syrian government’s claim that the uranium had come from Israeli missiles used to destroy the site in 2007. The report denounces Damascus for its lack of co-operation with the IAEA.

Together, the reports appear to bring closer the possibility of a military confrontation with Israel, which has said it will not tolerate a nuclear-armed Iran.

The IAEA report on Iran surprised many proliferation experts because it recorded a dramatic jump in Iranian stockpiles of low-enriched uranium (LEU) at the enrichment plant at Natanz. In its last report in November, the IAEA estimated that Iran had produced 635kg of LEU.

“Do they have enough LEU to produce a significant quantity of HEU [enough for a bomb]? Yes, if you count the U235 atoms then they do have a significant quantity,” an official close to the IAEA said.

“But it is theoretical and they would need to use their full capacity. They are not there yet. If they were to build another clandestine facility, then that would be different.”

David Albright, a veteran UN weapons inspector, who now heads the independent Institute for Science and International Security in Washington, gave a blunter assessment: “They have reached a nuclear weapons breakout capability. You can dance about it, but they would have enough to make 20-25kg of weapons grade HEU,” he said.

“If they break out they will do it at a clandestine facility, not at Natanz, so you can’t use Natanz as a measure of how fast they could do it.”