Davos, Switzerland ? Iran plans to begin work next month on an underground uranium enrichment facility, as part of a plan to create a network of tens of thousands of machines turning out material that could be used to make nuclear arms, U.N. officials said Friday.

The officials’ comments were the first concrete confirmation that work on the facility would begin in February. A senior U.S. State Department official warned the move would be a “major miscalculation” by Iran.

“If Iran takes this step, it is going to confront universal international opposition,” said Undersecretary of State Nicholas Burns. “If they think they can get away with 3,000 centrifuges without another Security Council resolution and additional international pressure, then they are very badly mistaken.”

Former Iranian President Akbar Hashemi Rafsanjani, meanwhile, accused the U.S. of acting like a bully, with the ultimate aim of forcing Iran to “abandon nuclear energy.” In a sermon in Tehran, he said a U.S. military buildup in the Gulf and the announcement that U.S. forces would seek to capture or kill Iranian agents in Iraq were aimed at Iranian nuclear programs.

“Today our enemies have come with several issues against us while having supporters in the world communities,” Rafsanjani told worshippers Friday. “This is bullying.”

Also Friday, the Iranian government said it would bar all U.N. inspectors from countries that voted in favor of a U.N. Security Council resolution last month that imposed sanctions on Iran for its nuclear program. Iran said it had rejected 38 names from a list of inspectors from the U.N. International Atomic Energy Agency.