iran has enriched enough uranium to make bomb, iaea says un nuclear watchdog's report says iran appeared to have slowed the rate at which enrichment capacity is expanding

The UN's nuclear watchdog reported today that Iran had managed to enrich a metric tonne of low enriched uranium (LEU), which UN officials say is technically enough to build a nuclear weapon.

UN officials cautioned that there remained many practical obstacles to the production of a bomb, and pointed out that the uranium was under close surveillance, and the report issued by the International Atomic Energy Agency (IAEA) said Iran appeared to have slowed down the rate at which its uranium enrichment capacity is expanding. But the report is likely to raise further the already high tensions surrounding the Iranian nuclear programme.

One respected US analyst said that the tonne milestone meant that Iran had reached "breakout capacity" - the theoretical ability to produce the 20-25 kg highly enriched uranium needed for one functioning warhead. Others were more cautious but said there was plenty more in the report to raise the level of international concern.

The IAEA said that Iran had put a roof over a "heavy-water" nuclear reactor being built near the town of Arak, capable and was preventing agency inspectors from carrying out ground inspections, meaning that they no longer had any way of seeing what was being done at the facility, which could potentially produce plutonium.

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 and where they are being installed.

In a separate report released at the same time, the IAEA said traces of uranium taken from the site of an alleged nuclear reactor in Syria were manmade and rejected the Syrian government's claim that the uranium had come from Israeli missiles used to destroy the site in 2007.

The report on the Dair Alzour site puts enormous pressure on Damascus as it rejects the Syrian explanation for the presence of uranium and denounces the government for its lack of cooperation with the agency's inquiry.

Together, the reports on Iran and Syria add greater urgency to international efforts to curb nuclear proliferation, and in particular, bring closer the possibility of a military confrontation between Iran and Israel, which has declared it will not tolerate Iran reaching nuclear weapons capability.

The IAEA report on Iran surprised many proliferation experts because, it recorded a dramatic jump in Iranian stockpiles of LEU at the enrichment plant at Natanz. In its last report in November, the IAEA estimated that Iran had produced 635 kg of LEU, based partly on Iranian government figures.

The agency now estimates that Iran had produced 839 kg of LEU by November, and that Iran had reported producing a further 171 kg in the following two months - a total of 1010 kg. The Iranian LEU has less than a 4% concentration of the fissile isotope Uranium 235. To make weapons grade HEU, with a concentration of 80-90%, it has to be further enriched, by being passed through massed 'cascades' of centrifuges.

"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 of HEU," a senior official close to the IAEA said. "But it is theoretical and they would need to use their full capacity to do so. They are not there yet. If they were to build another clandestine facility, then that would be different."

The official added that: "The nuclear material has been under containment and surveillance at all times."

UN officials also stressed that the number of centrifuges at Natanz actually being used to enrich uranium had increased relatively little since the last report in November, from 3,800 to nearly 4,000. But it also found a roughly 1,500 additional centrifuges had been installed and were "under vacuum", a preparatory step before enrichment can start.

David Albright, a veteran UN weapons inspector, who now heads the independent Institute for Science and International Security (ISIS) 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 20-25 kg of weapons-grade HEU," Albright 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. The Iranians have stopped telling the IAEA about the production of centrifuges ... so the agency doesn't know how many they are making."

Another western analyst, speaking on condition of anonymity, argued that due to the wastage involved in making a first nuclear device, Iran would need a few more hundred kilograms of LEU to reach breakout capacity, but added that the country appeared "well on its way" to that milestone.

Daryl Kimball, the head of the Arms Control Association in Washington argued that Iran's LEU stockpile was not the most worrying aspect of the new IAEA report.

"The report shows that Iran is slowly amassing an LEU stockpile but that stockpile we must remember is safeguarded. Iran can't divert that quantity without being very obvious," Kimball said.

"What should be of concern is that the IAEA is becoming less able to provide an accurate picture of what is going on. We don't know where centrifuges are being manufactured and whether they are being delivered to Natanz or somewhere else. And we cannot remotely see what is happening at [a] heavy water facility under construction at Arak, and whether that is being used for peaceful purposes."