"We have nothing more to add. This contamination came on imported equipment, so it is the third party or third country that should cooperate with the IAEA," foreign ministry spokesman Hamid Reza Asefi told reporters.

A report by the head of the International Atomic Energy Agencyreleased on Tuesday said agency inspectors had found more traces in Iran of highly enriched uranium that could be bomb-grade.

But Iran has consistently contended that such traces came into the country on equipment bought on an international black market originating in Pakistan.

The IAEA is pressing Pakistan to allow its inspectors access to verify Iran's insistence that the traces -- of uranium enriched to a level beyond that needed for civilian purposes -- were not from domestic enrichment activity.

But so far there is no sign that Iran's neighbour, which is not a signatory of the nuclear Non-Proliferation Treaty (NPT), will agree to a probe of its top-secret nuclear sites.

Neither Iran nor the IAEA have openly named Pakistan, but ElBaradei said in his report that despite the information received from Tehran and discussions with a third country, his agency was still not in a position to reach a conclusion.

The source of the contamination -- discovered by IAEA inspectors at three sites in Iran -- is one of the main outstanding issues the IAEA has with Iran, which denies US allegations it has a covert nuclear weapons programme.

But Asefi also accused IAEA chief Mohamed ElBaradei of "nit picking" in his latest report on Iran, released ahead of a June 14 meeting of the Vienna-based body's executive.

"This report has nothing new to say. It is a repetition of previous issues, but written in a different way," Asefi said, before complaining that the report had generated yet more suspicions.

"Rather than referring to our non-cooperation, the report is just nit-picking," he said, insisting ElBaradei's findings "show there is no evidence for keeping the file open."

The IAEA report also said Iran had admitted to importing parts for sophisticated P-2 centrifuges for enriching uranium, going back on claims that it had manufactured the parts domestically.

Washington has called on the IAEA, which has been investigating the Iranian programme since February 2003, to refer the Islamic republic to the UN Security Council for possible international sanctions.

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