"There can't be any stalling," Rice said in response to a question about U.S. efforts to get Russia and China to sign on to a strongly worded rebuke to Tehran.
Russia and China have refused to back a U.N. Security Council statement proposed by Britain, France and the United States demanding Iran suspend uranium enrichment.
Talks among the permanent members of the Security Council have bogged down over the statement, which traditional Iranian allies or trade partners see as a prelude to sanctions they do not support.
Rice planned to call her Russian counterpart Friday to try to break the deadlock.
The Security Council statement was intended to be an opening move in what could be lengthy talks at the powerful U.N. body over how to stop Iran from building a nuclear bomb.
The statement was also meant to be an easier pill to swallow for Russia and China than would another option: A tough Security Council resolution.
A presidential statement requires consensus from the body's 15 members. A resolution would be put to an up-or-down vote, meaning Russia and China would have to approve, abstain or veto action against Iran.
Rice indicated that the United States will not wait long before taking another tack.
"The international community has got to act," Rice said following a first meeting with the new Greek foreign minister, Theodora Bakoyannis.
"People are looking to the international community to show that this can, indeed, be dealt with diplomatically," Rice said. "We are committed to a diplomatic solution, but it has to be dealt with."
Russian deputy U.N. Ambassador Konstantin Dolgov said Russia was still under the assumption that the council was working toward a presidential statement, not a resolution.
"We are continuing negotiations in good faith and we hope that all our partners are doing likewise," Dolgov told The Associated Press.
The Iran nuclear file moved to the Security Council this month, with the support of veto-wielding members Russia and China. That was seen as a diplomatic victory for the United States, which had long sought to place Iran before the U.N. body for possible punishment.
Moscow and Beijing now insist the U.N. nuclear watchdog in Vienna, the International Atomic Energy Agency, play the lead role in clearing up suspicions over Iran's intentions.
"We think there is still an opportunity to get a compromise but a compromise that would send the right signal — endorse the IAEA, and help in the negotiation process which is going on and should go on," Dolgov said.
Iran says it is developing nuclear technology only to produce electricity, but the United States and its allies accuse the clerical regime of using civilian nuclear power as a cover to develop weapons.
"There is an erosion of confidence in Iran on this point, because they lied to the IAEA for 18 years," Rice said, referring to nuclear research and development activities that Iran kept hidden.
Russia and China have raised concerns that pushing Iran too hard could lead to its withdrawal from the Nuclear Nonproliferation Treaty and expulsion of IAEA inspectors.