The United States says it will take hard diplomatic work for the U.N. Security Council to impose sanctions on Iran for its failure to suspend nuclear enrichment activities.

Back in July, the United Nations Security Council passed a resolution that called on Iran to suspend its uranium enrichment program by August 31. Iran ignored the deadline, and on Wednesday, postponed a meeting in Vienna with officials with the European Union.

Undersecretary of State for Arms Control Robert Joseph

U.S. Under Secretary of State for Arms Control and International Security Robert Joseph told reporters in Washington the time has come to impose sanctions on Tehran.

"Iran continues to deny the IAEA access to facilities, individuals and to documents necessary to conduct the investigation," said Robert Joseph. "New questions raised about Iran's nuclear program have simply not been resolved, and the bottom line is that the IAEA is unable to confirm the peaceful nature of Iran's nuclear program."

Joseph said it would be intolerable if the United States and the international community allowed Iran to develop nuclear weapons.

"With nuclear weapons, Tehran would be more aggressive in its support for terror, and its subversion for peace and stability in Lebanon, in Iraq, in Afghanistan and elsewhere in the region," he said.

Joseph said Iran's possession of nuclear weapons would threaten the very existence of Israel, and trigger a nuclear arms race in the region that would threaten the future of the Nuclear Non-Proliferation Treaty.

He says despite the intelligence reports that Iran will not actually possess a nuclear weapon until at least the end of this decade, it is vital to prevent Tehran from developing the know-how.

"If we are talking about stopping Iran from acquiring nuclear weapons, we have to be able to stop them from acquiring the expertise, acquiring the technologies, that will lead them to a nuclear weapons capability," continued Robert Joseph.

Joseph says Nicholas Burns, the under-secretary of state for political affairs, will meet with officials from Britain, France, Russia, China and Germany in Berlin on Thursday to discuss the standoff.

Russia and China have advocated a slow approach to sanction, preferring diplomacy instead, but the United States sees U.N. sanctions a part of the diplomatic effort.