President Bush said Monday the United States will not waver in demanding that Tehran suspend all uranium enrichment-related activity before America would join international talks to resolve the nuclear standoff.

"Nuclear weapons in the hands of this regime would be a grave threat to people everywhere," Bush said on the eve of a trip to Europe.

Bush said the United States, Britain, France, Germany, China and Russia have adopted a unified approach to resolve the impasse with Iran diplomatically. He said that Iran must "fully and verifiably suspend its uranium enrichment and reprocessing activities" before the United States will join in negotiations with Iran.

"Iran's leaders have a clear choice: We hope they will accept our offer and voluntarily suspend these activities so we can work out an agreement that will bring Iran real benefits," the president said. "If Iran's leaders reject our offer, it will result in action before the Security Council, further isolation from the world and progressively stronger political and economic sanctions."

Bush spoke at the commencement ceremonies of the U.S. Merchant Marine Academy, 20 miles east of Manhattan.

On Sunday, Iran accused the United States of steering Europe away from a possible compromise on Tehran's disputed nuclear program. Iran's foreign ministry said the U.S. insistence on conditional negotiations over a Western package of incentives has narrowed the scope of possible talks and made it tougher for all parties to reach a solution.

The incentives are meant to persuade Iran to stop enriching uranium, a process that can make nuclear fuel for a power plant or fissile material for an atomic bomb. Iran says enriching uranium is its country's unalienable right, and that it is reviewing the package and will propose amendments to the deal.

CountryWatch: Iran

"I have a message for the Iranian regime," Bush said. "America and our partners are united. We have presented a reasonable offer. Iran's leaders should see our proposal for what it is: an historic opportunity to set their country on a better course. If Iran's leaders want peace and prosperity and a more hopeful future for their people, they should accept our offer.

"Abandon any ambitions to obtain nuclear weapons and come into compliance with their international obligations," he said.

European Union foreign policy chief Javier Solana presented the package of perks and possible penalties to Tehran on June 6. The package was drawn up by the five permanent members of the U.N. Security Council — the United States, Britain, China, France and Russia — and Germany.

The package calls on Iran to suspend, not permanently halt, uranium enrichment as a condition for the start of talks, although the negotiations are aimed at achieving Iranian acceptance long-term moratorium on such activities.

Bush is the first American president to address a graduating class at the academy. The president's former White House chief of staff, Andrew Card, who studied at the academy, and hitched a ride on Air Force One to attend the event.

Bush noted that Card received a warmer welcome than when he attended the academy in the 1960s. "When he was a plebe, he was stuffed in a duffle bag and run up the flagpole," Bush said.

Bush's decision to make the academy the site of his fourth and final commencement address this year helps raise the profile of the little-known school.

Kings Point graduates work as deck officers aboard container ships, oil tankers, passenger cruise ships and other vessels. Others remain on land and have become engineers in shipbuilding companies and work in a variety of port operations, including security, while some opt for military careers.