Israel has said that the fuelling of Iran's first nuclear reactor is "totally unacceptable" and urged greater world pressure to force Tehran to stop any further uranium enrichment.
Iranian engineers reportedly began loading fuel into the country's first nuclear power plant with the help of Russia on Saturday, marking a milestone in Tehran's development of what it insists is a peaceful nuclear energy program.
"It is totally unacceptable that a country that so blatantly violates international treaties should enjoy the fruits of using nuclear energy," Fox News quoted Israeli Foreign Ministry spokesman Yossi Levy, as saying in a statement.
On Saturday, the United States sent a calming message to Israel stating that the new reactor was designed for peaceful purposes for producing electricity and does not threaten Israel.
The Iranians have said they need additional nuclear reactors to produce electricity to meet the country's population growth and development rate, particularly in light of its declining reserves of oil and gas. Theoretically, however, the reactor has the potential to provide another source of fissionable material that could be used for nuclear weapons.
Currently the main concern about the country's nuclear weapons program is the enrichment activity at Natanz and perhaps at a secret unknown location.