VIENNA, September 7 (RIA Novosti) - The head of the United Nations nuclear watchdog said on Monday the organization had reached a "stalemate" with Iran over its nuclear program.

Addressing the 35-nation board of the International Atomic Energy Agency (IAEA), Mohamed ElBaradei acknowledged that Tehran has improved cooperation with his agency only on control over activities at its main nuclear facility in Natanz and an IR-40 research reactor at Arak.

"On all other issues relevant to Iran's nuclear program, however, there is stalemate," ElBaradei told the IAEA board, adding that Iran continued to enrich uranium in defiance of three sets of UN sanctions.

Western powers suspect Iran's uranium enrichment is aimed at developing nuclear weapons. Tehran denies the allegation, saying its nuclear program is for electricity production only.

Mohamed ElBaradei again urged the Islamic Republic to clarify all outstanding issues in the dispute over its nuclear program and implement the provisions of the Additional Protocol to the Nonproliferation Treaty (NPT).

"It is essential that Iran substantively re-engage with the agency to clarify and bring to closure all outstanding issues," he said.

In July, the G8 countries urged Tehran to discuss by September trade benefits that could be offered in exchange for abandoning nuclear enrichment, to avoid harsher sanctions.

Iranian President Mahmoud Ahmadinejad said on Monday his country would continue to work in the framework of global regulations and in close cooperation with the International Atomic Energy Agency, but ruled out talks on Iran's nuclear plans with the Iran Six - a group of international mediators comprising the United States, France, Britain, Russia, China and Germany.

Western powers seek harsher sanctions against the Islamic Republic if it does not agree to halt uranium enrichment. Russia and China, however, insist on diplomatic steps.