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U.N. Secretary-General Ban Ki-moon expressed "grave concern" to Iran's president late Friday over Tehran's activities related to the construction of a new uranium enrichment facility.
Ban's office said in a statement from New York it is very concerned over Iran's activities related to uranium enrichment, including construction of the new plant.
Ban emphasized that the "burden of proof is on Iran" and called on Tehran to fully implement relevant U.N. Security Council resolutions and cooperate with the IAEA (International Atomic Energy Agency) to resolve all concerns related to its nuclear program.
A number of world powers, including Russia and China, also urged Iran on Friday to cooperate with the IAEA on any probe of its newly revealed uranium enrichment facility.
Russian President Dmitri Medvedev said in a statement that disclosure of the site is cause for "serious concern."
He once again implied that Russia might support sanctions if Tehran fails to comply with the world's demands that it halt uranium enrichment. Without mentioning specifics, Medvedev said that if "cooperation does not work, other mechanisms" should be used.
He demanded that Iran demonstrate evidence of its peaceful nuclear intentions at an October 1 meeting with six world powers including Russia.
A Chinese spokesman said Beijing is following the situation closely.
Russia and China are two of the five permanent members of the United Nations Security Council, but have historically been more reluctant than the United States and European nations to punish Iran for enriching uranium.
Also Friday, Egypt's foreign minister, Ahmed Aboul Gheit, told the Associated Press news agency that a nuclear-capable Israel and an Iranian government actively pursuing nuclear weapons could trigger a nuclear arms race in the Middle East.
U.S. President Barack Obama and other Western leaders have insisted the IAEA gain immediate access to the facility to ensure it is not being built to produce atomic weapons.
The Security Council has passed three sets of sanctions urging Iran to halt uranium enrichment, a process that can be used to make nuclear weapons.
Some information for this report was provided by AFP, AP and Reuters.