The United States said Wednesday it would join in face-to-face talks with Iran over its disputed nuclear program once Tehran puts its atomic activities on hold, a shift in tactics meant to offer the Iranians a last chance to avoid punishing sanctions.

The U.S. wants a "positive relationship" with Iran, Secretary of State Condoleezza Rice said. [AP]

Iran dismissed the offer as "a propaganda move."

At the White House, President Bush said that the U.S. would take a leading role in solving the conflict and that it was important to do so diplomatically.

"Our message to the Iranians is that one, you won't have a weapon, and two, that you must verifiably suspend any programs, at which point we will come to the negotiating table to work on a way forward," Bush said.

Before leaving for meetings in Europe on Iran, Secretary of State Condoleezza Rice said that while the U.S. was willing to join talks between European nations and Iran, it was also helping to prepare a package of sanctions that Tehran could face should it decline the new offer.

"We're prepared to go either way," Rice said

The overture to join stalled European talks came after mounting pressure on the U.S. from European allies.

The administration is convinced Russia and China would support sanctions or other harsh measures if new talks fail to persuade Iran to abandon nuclear efforts that the West fears could lead to a bomb, said a senior administration official. The official briefed reporters on condition of anonymity because the secretary was continuing talks with other countries.

Rice will be working to reaffirm such support on Thursday.

The Iranian news agency said Iran accepts only proposals and conditions that are in the nation's interest. "Halting enrichment definitely doesn't meet such interests," IRNA said.

The United States has had no diplomatic ties with Iran and few contacts at all with its government since Islamic radicals took over the U.S. Embassy in 1979 and held diplomats for more than a year.

Rice will meet with foreign ministers from the other permanent U.N. Security Council members on Thursday in Vienna to finalize a package of economic incentives and threats to be presented to Tehran. That package would be on the table in any new talks involving the United States.

The Bush administration had until now refused to talk directly to the Iranians about their nuclear program, although there have been sporadic contacts among relatively low-level officials on other subjects. The U.S. has long rejected direct contacts because it says Tehran supports terrorism and because it wants to avoid appearing to legitimize the regime.

The offer to talk should strip Iran and some U.S. allies of the argument that the hardline U.S. stance was an obstacle, or that Washington was not willing to try every means to resolve the impasse peacefully, U.S. officials said.

"This is the last excuse, in some sense," Rice said.

She said the United States was not offering full diplomatic relations with Iran and would not swear off ever using military action to stop what the U.S. contends is a rogue program to build a nuclear weapon.

"This is not a grand bargain," Rice said. "What we're talking about here is an effort to enhance the chances for a successful negotiated solution to the Iranian nuclear problem."

The administration has given arms-length support to European efforts to bargain with Iran, but also has been the prime mover for sanctions or other tough United Nations action. Russia and China, Iran's commercial allies on the council, have so far blocked that path.

Rice would not directly answer questions about whether those nations are committed to tough measures if the U.S. overture doesn't work.

She spoke of "tactical differences" and said, "I think you can be sure that our friends and our partners understand the importance of the step and the importance that the Iranians must now see of making a choice and making that choice clearly."

In New York, the U.N. ambassadors from China and Russia said the U.S. announcement showed it is more serious about finding a diplomatic solution to the dispute. Chinese Ambassador Wang Guangya added that Washington's offer to talk to Iran should be unconditional.

In Brussels, Belgium, European Union foreign policy chief Javier Solana welcomed the U.S. words. "Direct U.S. participation would be the strongest and most positive signal of our common wish to reach an agreement with Iran," he said.

British Foreign Secretary Margaret Beckett said, "The European side's goal is to present a serious and substantial offer of cooperation, which demonstrates to Iran the benefits that would flow from compliance ... rather than the further isolation which would result from their failure to do so."

The U.S. offer is conditioned on Iran suspending its enrichment of uranium and related activities and allowing inspections to prove it. European nations and the Security Council have demanded the same thing, but Iran has refused to comply.

Iran did suspend enrichment activities while talks were active with the Europeans last year but resumed and stepped up the program this spring.

Uranium enrichment can led either to a bomb or to nuclear power production, and Iran has so far insisted that it won't take any deal that involves giving up that technology.

If Iran agreed to suspend disputed activities in order to talk with the United States, it could still insist on resuming them later, which U.S. officials say would be a deal-breaker.

At that point, the United States and its allies would be expected to move for tough U.N. action, possibly including economic or other sanctions.