"The United States will not be at the table for any negotiations absent a suspension as outlined by the IAEA and the (UN) Security Council," State Department spokesman Sean McCormack said at a briefing.

"That means there has to be a verifiable suspension, and suspension means suspension means suspension. There is a definition listed, I think, in the IAEA Board of Governors statement from several months back," McCormack said.

The United States has accused Iran of trying to develop nuclear weapons under the cover of civilian nuclear programs and has sought to impose sanctions on Iran through the UN Security Council. However, Iran has said that its nuclear programs are for peaceful purposes only.

The European Union (EU) has tried to solve Iran's nuclear issue through negotiations. Reports said that the EU and Iran are now close to agreement that would include a suspension of uranium enrichment.