Vienna, Feb. 24 (Reuters): The UN nuclear watchdog said today it still had questions about Iran’s nuclear programme despite what Tehran called a full disclosure last October, and diplomats said Iran was being difficult.

Inspectors for the International Atomic Energy Agency (IAEA) said in a report Iran had agreed at the last minute to freeze more activities related to enriching uranium but said several questions remained open.

Those open questions included why Iran had not declared its possession of designs for advanced P2 enrichment centrifuges and its past experiments aimed at creating polonium, a substance used to initiate a chain reaction in nuclear explosions.

The report, sent to the IAEA board and obtained by Reuters, also said a combination of highly enriched and low-enriched uranium had been found at two sites in Iran and had not yet been fully explained. The mixed contamination was a “major outstanding issue”, the IAEA said.

“Until this matter is satisfactorily resolved, it will be very difficult for the agency to confirm that there has not been any undeclared nuclear material or activities,” the report said.

Iran has explained uranium traces found by IAEA inspectors as the result of contaminated centrifuges it bought on the black market. “If it was all imported from one place, why are there different types of contamination at Kalaye and Natanz?” asked one Vienna-based diplomat who follows the IAEA.

The IAEA said Iran’s failure to acknowledge that it had designs for the P2 centrifuge was “a matter of serious concern”.

Centrifuges are used in uranium enrichment, a process of purifying uranium for use in weapons. Iran gave the IAEA last October what Tehran called a full declaration of all its nuclear activities.

The US says Iran’s nuclear programme is a front for building nuclear weapons.