US may initiate UNSC action against Iran

"They shouldn't do it because it would really be a sign that they are not prepared to actually make diplomacy work," Rice told reporters.

"In terms of the next phase, if negotiations have been exhausted, we have the votes, there is a resolution sitting there on the Security Council, we'll vote it," she said.

Rice declined to give a timeline for such action but said "the Iranians are digging their own hole of isolation deeper and deeper."

Her remarks here came as Iranian delegates failed to show up at the headquarters of the UN atomic watchdog, the International Atomic Energy Agency, in Vienna Thursday for a scheduled meeting to discuss Tehran's plan to resume atomic fuel research, which was suspended two years ago.

Tehran has described the plan as a "programme for peaceful nuclear energy". It has said it will re-start the programme on Monday.

The plan was revealed in a letter Tuesday to the IAEA, prompting the world nuclear watchdog to seek "clarifications".

The European Union and the United States fear Iran's civil nuclear programme could provide cover for developing a nuclear bomb. Tehran denies the accusation, insisting the programme is designed solely to meet its electricity needs.