United Nations nuclear agency officials meeting Friday in Vienna with representatives from Iran failed to reach agreement over access to a disputed nuclear site the West suspects is related to possible nuclear weapons development.

The two sides have been in periodic negotiations for months over access to Iran's Parchin nuclear site, a military installation southeast of Tehran that the International Atomic Energy Agency says may have been a testing ground for the making of a nuclear warhead.

After seven hours of talks, Herman Nackaerts, the International Atomic Energy Agency's chief inspector, told journalists that “important differences remain between Iran and the U.N.” and there are no plans for another meeting.

News reports quoting comments from the IAEA in recent days express fears that Iran is ramping up its work on developing nuclear arms by installing new uranium enrichment centrifuges at another site, the Fordow underground facility.

Iran says its nuclear ambitions are peaceful.

The talks come as representatives of nearly 120 nations, including dozens of heads of state, are to convene in Tehran on Sunday for the summit of the Non-Aligned Movement.

The Non-Aligned Movement is an organization formed during the Cold War to provide a forum for countries that were not officially allied with either the United States or the Soviet Union.

The U.S. State Department says Iran will try to manipulate the Non-Aligned Movement at the summit and try to divert attention from its defiance of several U.N. Security Council resolutions and international sanctions over its disputed nuclear programs.