Iran must address “serious concerns” about “possible military dimensions” to its nuclear programme after significantly escalating its ability to enrich uranium, the International Atomic Energy Agency said yesterday.

The latest report by United Nations experts disclosed a 42 per cent rise in the number of operational centrifuges enriching uranium inside the Natanz facility in the last four months.

Work inside a second, previously secret enrichment plant has also been stepped up, with 698 centrifuges operating inside the Fordow installation near Qom, a 69 per cent increase on the number recorded during the last inspection in October.

Meanwhile, the IAEA said that Iran had declined to offer full co- operation to its inspectors when they visited the country earlier this month. In particular, they were prevented from visiting a military location at Parchin, where experiments that would only be relevant to mastering the detonation system of nuclear weapons are understood to have been conducted. It bemoaned bemoaned "major differences" with Iran after two fruitless visits.

Guido Westerwelle, the German foreign minister, said that he was “very concerned about the latest report from the IAEA”, adding: “We think Iran should understand the key to ending sanctions is in their own hands: they have a duty to co-operate with the international community.”

The latest report by the IAEA is likely to deepen Israel’s fears about Iran’s intentions, particularly the build-up of centrifuges in the Fordow facility, which is dug into a mountainside and could be immune from military attack.

The IAEA reported that 8,808 centrifuges were functioning inside Natanz, compared with 6,208 on its last visit, although the report cautioned that not all of the machines may have been working. Iran’s experts had also installed the casings for another 6,177 centrifuges.

Six UN resolutions say that Iran should stop enriching uranium, a highly sensitive process that could be used to make the essential material for a nuclear weapon.

This sudden rise in the number of operational centrifuges shows that, on the contrary, Iran is stepping up its enrichment capacity.

However, the IAEA also reported that all of the machines in the main enrichment halls of both Natanz and Fordow were older IR-1 models, contradicting claims by Iranian officials, including President Mahmoud Ahmadinejad, that the country’s experts were now operating large numbers of more advanced models.

The report voiced disappointment about the last official visit by inspectors to Iran, noting that they were denied access to a key location and that no agreement had been reached on how to resolve any of the outstanding issues.

“As Iran is not providing the necessary co-operation, including by not implementing its additional protocol, the agency is unable to provide credible assurance about the absence of undeclared nuclear material and activities,” said the report.

Consequently, the IAEA was unable to “conclude that all nuclear material in Iran is in peaceful activities.” Instead, the IAEA “continues to have serious concerns regarding possible military dimensions to Iran’s nuclear programme.”

Yukiya Amano, head of the IAEA, urged Iran to “address the agency’s serious concerns” and allow inspectors to visit Parchin.

However, Vladimir Putin, the Russian prime minister, said that Western concern about Iran’s nuclear ambitions was a cover for the real objective of toppling the Tehran regime. (© Copyright of Telegraph Media Group Limited 2012. 02/25/12)