They made their calls on Sunday in contrast to the president's multilateral approach through the UN.

US Secretary of State Condoleezza Rice said the Security Council would have to look at options to compel Iran to "obey the international system".

But Richard Lugar, the Republican chairman of the Senate foreign relations committee, said it was too soon to press for sanctions.

The UN Security Council is due to meet later this month to discuss Iran, which has announced its successful production of enriched uranium.