The US ambassador to the United Nations says the international community will be watching closely to ensure that Tehran fulfills the commitments it made during a landmark meeting in Geneva last week.

Speaking on NBC's "Meet the Press," Susan Rice said Iran is now showing some encouraging signs of openness about its nuclear program. But she said these are "only the beginning."

Rice added that Washington and other veto-holding permanent members of the UN Security Council are studying sanction options, if Iran fails to prove that its nuclear program is for peaceful purposes.