Iran has expanded its uranium enrichment activities in defiance of UN demands to scrap its nuclear-related programs, a confidential report of the international nuclear watchdog said on Wednesday.

The International Atomic Energy Agency (IAEA) said in the report that it worried about the situation and could not provide assurances about the "exclusively peaceful nature" of Iran's atomic program.

The report from Mohamed ElBaradei, the head of the IAEA, also expressed concern about its "deteriorating" understanding of unexplored aspects of the program.

The report, which was posted on the IAEA internal website, blamed Iran for blocking IAEA efforts to probe its nuclear activities. It was handed over to the UN Security Council president for distribution among its members.

The West has been worried about Tehran's nuclear ambitions, accusing the country of clandestinely trying to develop a nuclear bomb. Iran has claimed that it has the right to use atomic energy for generating electricity.

Iran is still under a second set of sanctions from the UN Security Council aiming to put the country's atomic activities to a halt. The first sanctions were imposed on Dec. 23.