Iran signed a surprise deal for a nuclear fuel swap with Western nations Monday, brokered by Brazil and Turkey. It was the first such agreement by the Islamic Republic with foreign nations since 2004.

The unexpected pact is aimed at assuaging international concerns over Iran's nuclear program and could provide an alternative to tough new sanctions against Iran that have been proposed by the United States and other Western powers. It will bring the discussions over the nature of the Iranian nuclear program into a new phase, analysts said, and presents the United States and a coalition of mostly Western nations with a new bloc of developing countries that are supportive of Iran's nuclear program.

In Washington, the White House acknowledged the efforts by Brazil and Turkey but said the proposal "must now be conveyed clearly and authoritatively" to the International Atomic Energy Agency (IAEA) before the international community can consider it.

"Given Iran's repeated failure to live up to its own commitments, and the need to address fundamental issues related to Iran's nuclear program, the United States and international community continue to have serious concerns," White House spokesman Robert Gibbs said in a statement.

The deal involves Iran sending a large part of its stockpile of low-enriched uranium to Turkey as a trust-building measure, possibly within one month. Diplomats here said the move is aimed at proving that Iran has no intention of using the material to build a nuclear weapon.

Under the accord, Iran's uranium would stay in Turkey as official Iranian property until the Islamic Republic received in exchange a batch of higher-enriched uranium, which it would use -- under IAEA supervision -- in a 42-year-old, U.S.-built research reactor that produces medical isotopes.

The deal widens a divide between a group of countries led by the United States, on the one hand, and some developing nations on the other, over the right of Iran and other developing countries to use nuclear energy.

Countries such as Brazil and Turkey, but also Egypt and Indonesia, increasingly view the Western-led debate over Iran's nuclear program as an important test case for their own nuclear ambitions. While the United States and its allies say they fear nuclear weapons proliferation, some developing nations say that world powers are determined to control nuclear technology and want to prevent the development of independent nuclear energy programs.

In announcing the new deal, Brazilian Foreign Minister Celso Amorim and his Turkish counterpart, Ahmet Davutoglu, condemned any new sanctions against Iran and said Iran has a right to a "full nuclear fuel cycle, including enrichment."

"This plan is a route for dialogue and takes away any grounds for sanctions," Amorim told reporters in Tehran. In an earlier interview, he said that it is time for Western nations to come to terms with the fact that Iran has a nuclear program.

In the White House statement, Gibbs said the transfer of Iran's low-enriched uranium off its soil, as it agreed to do in October, "would be a positive step." But he noted that Iran still insists on enriching some of its uranium to 20 percent in "direct violation of U.N Security Council resolutions." Gibbs recalled that Iran originally justified producing the more highly enriched uranium to meet the needs of its Tehran Research Reactor, which now would be fueled by uranium received in the swap.

He said the accord announced Monday is "vague" about Iran's willingness to meet with the six world powers that have been negotiating with Tehran on its nuclear program.

"The United States will continue to work with our international partners, and through the United Nations Security Council, to make it clear to the Iranian government that it must demonstrate through deeds -- and not simply words -- its willingness to live up to international obligations or face consequences, including sanctions," Gibbs said. "Iran must take the steps necessary to assure the international community that its nuclear program is intended exclusively for peaceful purposes, including by complying with U.N. Security Council resolutions and cooperating fully with the IAEA. We remain committed to a diplomatic solution to the Iranian nuclear program . . . and will be consulting closely with our partners on these developments going forward."

Germany, said the swap deal, which still needs the approval of the United States, Russia and France, does not free Iran from U.N. Security Council demands that it immediately stop enriching uranium.

The agreement announced in Tehran on Monday builds on a swap deal Iran struck in October with the "Vienna group" -- a negotiating bloc that consists of the United States, Russia and France and representatives of the IAEA.

That pact fell apart after Iran insisted that any swap must take place on Iranian soil and be carried out in batches or simultaneously. The failure prompted the Obama administration to back off its policy of engagement with the Islamic Republic.

The big difference now is that Iran -- facing tougher sanctions -- has severely compromised on its demand that the swap take place within its borders. It is now prepared to send 2,640 pounds of low-enriched uranium to neighboring Turkey and to wait up to a year for the delivery of higher-enriched fuel from Russia and France.

If, for any reason, the swap fails, Iran's stockpile would be returned by Turkey, Davutoglu said.

The amount of low-enriched uranium agreed upon in the new deal, however, is significantly lower than the 70 percent of Iran's stockpile that U.S. officials have said they expect to be sent abroad.

An unnamed State Department official told Reuters news agency on Monday that 70 percent of the stockpile would equal nearly 4,400 pounds. In February, 70 percent of the stockpile was estimated at between 3,179 and 3,828 pounds.

The head of Iran's Atomic Energy Agency, Ali Akbar Salehi, in an interview said the increase was "insignificant." Iran's Foreign Ministry spokesman also stated that Iran would not stop enriching its uranium up to 20 percent, a controversial move that Iran started after the first swap proposal failed.

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