The United States says it hopes to discuss with other world powers Tuesday in Moscow steps they can take in response to Iran's defiance of the U.N. Security Council over its nuclear program. Diplomats from the five permanent U.N. Security Council member states and other countries convene for two days of meetings in the Russian capital.

The meeting was originally intended to lay groundwork for security talks at the July summit of the G-8 leading industrial powers in St. Petersburg.

But it has been expanded to include Chinese and European Union diplomats and it looms as a key preliminary meeting for the expected U.N. Security Council debate on the Iranian nuclear issue next month.

Iran has given no indication that it intends to heed the non-binding president's statement by the council at the end of March calling on it to end uranium enrichment activity and return to negotiations over its nuclear program.

The Security Council convenes April 28th to hear a situation report by International Atomic Energy Director General Mohamed ElBaradei, after which U.S. officials say it will have to decide how to respond to what they say has been belligerent Iranian behavior.

The U.S. team in Moscow is headed by the third-ranking State Department official, Undersecretary for Political Affairs Nicolas Burns. At a news briefing, State Department Spokesman Sean McCormack said Burns will try to build a consensus for a strong message to Iran that could take the form of any of a number of punitive measures:

"Part of what we're looking at, and part of what will be on the table for discussion when Undersecretary Burns travels to Moscow will be things like U.N. resolutions, Chapter Seven resolutions, things like asset freezes, thing like sanctions, things like travel restrictions. So I'm not going to try to pre-judge an outcome at this point. But that's certainly what's on the table as far as we're concerned as well as, I would say, others as well," he said.

Both Russia and China, who wield veto powers in the Security Council, have said in advance of the Moscow meeting that they oppose sanctions against Iran.

Spokesman McCormack said the Moscow meeting is not intended as a decision-making session, but rather as venue to in his words tee up or raise ideas for a possible international response.

He said there are punitive measures that could be taken outside the framework of the Security Council, noting that the European Union has decided to consider the idea of travel and other penalties against the Iranian leadership.

McCormack conceded that the United States, which lacks diplomatic ties with Tehran and already has sanctions in place, has little else it could do, other than ban imports of a handful of Iranian goods such as oriental rugs and pistachio nuts that had been authorized by the Clinton administration.

Iran denies U.S. charges it has a secret nuclear weapons program, but since the March 29 Security Council statement it has trumpeted advances in uranium enrichment for its nominally-peaceful nuclear program.

Bush administration spokesmen expressed concern over an Iranian claim Monday that it was conducting research on the so-called P-2 uranium centrifuge, an advanced enrichment device for which U.S. officials say Iran may have acquired technology from the proliferation ring of Pakistani scientist A.Q. Khan.

The White House said Iranian work on P-Two centrifuges would be of very serious concern and a further violation of Iran's international nuclear safeguard obligations.