Western diplomats have expressed concern over Iran's move to enrich uranium to a higher level, saying it violates United Nations sanctions resolutions over Tehran's nuclear program.

Diplomats from the United States, Britain, France and Germany raised the new developments at the U.N. Security Council Wednesday, two days after Iranian officials confirmed that a new underground complex has started refining uranium.

Britain's U.N. deputy ambassador, Philip Parham, said enrichment at the Qom facility was “a further clear breach” of Security Council resolutions passed on Iran.

Miguel Berger, Germany's deputy U.N. ambassador, called the Iranian decision “a step of escalation,” while U.S. Deputy Ambassador Rosemary DiCarlo said Iran has “no justification for enriching uranium at this level.”

The Security Council has imposed four sets of sanctions on Iran for refusing to stop enrichment work, which has civilian and military uses. Later this month, the European Union will discuss a possible oil export embargo to further pressure on Iran.

Iran is now threatening to close the Strait of Hormuz, a vital waterway for the global oil trade. U.S. Secretary of State Hillary Clinton said Wednesday that Iran's threat to do so is “provocative and dangerous.” She urged Iran to end its “provocative behavior” and its search for nuclear weapons.

“I think it's important to recognize very clearly that the provocative rhetoric coming out of Iran in the last week has been quite concerning.”

Western powers accuse Iran of trying to develop a nuclear weapon. Tehran says its nuclear ambitions are peaceful.