BERLIN,(Reuters) – U.N. inspectors have discovered new traces of highly-enriched uranium on nuclear equipment in Iran, deepening suspicions Tehran may still be concealing the full extent of its atomic enrichment programme, diplomats said.

Several Western diplomats said there were signs Iran continued to pursue uranium enrichment research in secret and fear the goal is to acquire the capability to produce enriched-uranium fuel for weapons –a charge Iran denies.

In its April report to the U.N. Security Council, the International Atomic Energy Agency (IAEA) said it took samples from equipment that had been acquired by a former research centre at Lavizan-Shiyan. The centre was razed in 2004 before IAEA inspectors could examine it.

The IAEA inspectors took swabs from the machinery earlier this year which were subjected to microscopic particle analysis.

“Preliminary analysis by the IAEA showed traces of highly-enriched uranium in the samples,” a Western diplomat accredited to the IAEA told Reuters on condition of anonymity. He gave no details about the equipment. The former physics centre at Lavizan, which advised the defence ministry, acquired some dual-use machinery useable for uranium enrichment.

A diplomat in Vienna, where the IAEA is based, confirmed the new finding but warned against exaggerating its significance: “It’s no smoking gun. There could be many explanations. But it increases pressure on Iran to come clean about Lavizan.”

Iranian officials declined to comment for this article.

In 2003, the IAEA found traces of highly-enriched uranium (HEU) at several sites in Iran. Most HEU is now believed to have come from contamination on second-hand Pakistani equipment.

“Even if it is the same contamination, this is a significant finding because it indicates something was going on at Lavizan,” said David Albright, a former U.N. weapons inspector and head of the Institute for Science and International Security think-tank.

He said it raised the question of whether Iran ran a second parallel enrichment programme alongside the one it has declared.

The finding will probably also deepen suspicions among Western countries that Iran’s military was actively involved in the programme for uranium enrichment, a process of purifying uranium for use in nuclear power plants or atomic weapons.

Iran says it only wants to generate electricity, but the West believes the secrecy and military links to its atomic programme are clear signs that it is also aimed at making bombs.

The U.N. Security Council has called on Iran to freeze its enrichment programme, but Tehran refuses.

Iran has already succeeded in purifying uranium to low-grade levels needed for power plants. Western diplomats say the sophistication of Iranian nuclear scientists is surprising.

They say that during a 2-1/2 year suspension of its enrichment programme, Iranian scientists have significantly improved their mastery of centrifuges, which purify gas of a uranium compound by spinning at supersonic speeds.

“Our (intelligence) assessment is that you cannot explain Iran’s progress without secret (enrichment) sites being involved,” said a diplomat from a country critical of Iran.

Others say Iran could have made such progress through simulation work.

Another diplomat from the same country said he suspected small amounts of processed uranium gas were being diverted from Isfahan, possibly to undisclosed enrichment sites in Iran. An EU diplomat said the IAEA had such suspicions too but no proof.

Albright said there was no proof of any “secret site” in Iran.