"What is clear is that it is highly unlikely that Iran is going to accede to the demands of the international community," Ms. Rice said at the opening of a conference of envoys from NATO and the European Union. She added that "in order to be credible the Security Council of course has to act."
The United Nations' credibility is at stake, Ms. Rice said, and "it cannot have its word and its will completely ignored by a member state."
Despite her tough words, it was far from clear whether Russia would drop its opposition to a resolution at the Security Council that would implicitly threaten sanctions. The United States wants a resolution criticizing Iran under Chapter 7 of the United Nations charter, a provision that implies that sanctions are possible if it is flouted.
Past opposition by Russia, China and others has forced the United States to back down from its demand for such a resolution, but now American and European diplomats hope that a new critical finding by the International Atomic Energy Agency will bolster support for the action it wants.
Such a report is expected Friday by the agency in Vienna. Iranian officials have been meeting with agency officials in the last few days, but they do not appear to have changed the situation, diplomats at the agency said.
Iran insists that its activities are for peaceful purposes only, and its leaders have kept up a steady volley of criticism of the United States, Europe and others suspecting it of having a weapons program, even while Iranian envoys have met with international atomic agency inspectors this week.
Ms. Rice arrived in Bulgaria Thursday afternoon after conferring with Iraqi leaders in Baghdad along with Defense Secretary Donald H. Rumsfeld. The occasion was a session of more than 30 envoys representing countries in both NATO, which is a military alliance, and the European Union, a political and economic body.
Though the issue of Iran was not on the formal agenda, it loomed over most other matters because of the escalating threats and Iran's defiance. Many in Europe are worried that the United States plans to carry out a military strike against Iran as it did against Iraq.
A Bulgarian journalist, citing the news that the United States and Bulgaria plan to sign a basing agreement on Friday allowing American forces to use military centers in this country, asked Ms. Rice if the agreement would require Bulgarian permission for any American troop deployment from such a base.
He did not mention Iran, but Ms. Rice felt compelled to assuage Bulgarian feelings by saying that the United States was still concentrating on getting a diplomatic or political solution to the Iran confrontation and did not contemplate military action. Any such action, she said, would be done in cooperation with Bulgaria, she said.
In a speech northwest of Tehran today, President Mahmoud Ahmadinejad was defiant, saying his country would not give up its right to pursue its nuclear activities, even if sanctions or other punitive measures are imposed.
"We want nuclear technology for peace and progress of nations and if some believe that they can prevent us with psychological warfare and resolutions, they are mistaken," Mr Ahmadinejad said in a speech in northwest Iran that was reported on the ISNA news agency.
"Our people have mastered the nuclear technology and no one can take it away from them," the president added.
Iran's supreme religious leader vowed Wednesday that Iran would retaliate "twofold" if it were attacked by the United States over its refusal to comply with demands regarding its nuclear activities.
"Iranian people and the Islamic regime will not invade any country, but the Americans should know that if they invade Iran, their interests around the world would be harmed," the supreme leader, Ayatollah Ali Khamenei, told workers gathered ahead of May Day, the international workers' holiday.' "Iran will respond twofold to any attack."
