(CNN) -- Iran appeared to make a concession in its long-running dispute with the international community Monday, only to throw a potential spoiler into the mix soon after.
Tehran said it had agreed to send thousands of pounds of low-enriched uranium, which was produced in Iran, to Turkey in exchange for highly-enriched uranium.
But then Iran said it intended to continue enriching uranium to the level that can sustain nuclear reactions, a move the United States and its allies do not want Tehran to make.
"We are not planning on stopping our legal right to enrich uranium," Iran's Foreign Ministry spokesman Ramin Mehmanparast told CNN by telephone.
The deal between Iran and Turkey had been designed to answer international concerns that Iran was secretly trying to build nuclear weapons -- a charge it has long denied.
Mehmanparast said the United States and its allies should accept the proposal.
"I don't think there's any reason why any country would reject this agreement," he said. "This agreement is based on the same requirements and criteria as the previous proposal. This is what they had asked for. If they come back and say no then it will show they are not serious about reaching an agreement."
White House press secretary Robert Gibbs said Monday the agreement will not halt the U.S. push for stronger sanctions against Iran.
"It does not change the steps that we are taking to hold Iran responsible for its obligations, including sanctions," Gibbs said at the daily White House news briefing.
Ali Akbar Salehi, the head of Iran's Atomic Energy Organization, said he hoped the deal would lead the United Nations nuclear energy watchdog to close its file on Iran "forever."
His speech was carried live by Iran's government-backed Press TV.
The United States was in close contact with Turkish diplomats who helped broker the deal, a U.S. official following Iranian affairs told CNN. The official was speaking on condition of anonymity.
U.S. Secretary of State Hillary Clinton and National Security Advisor James Jones were "feverishly workings the phones" Sunday night, discussing the proposed nuclear deal with Turkey's Foreign Minister, Ahmet Davutoglu, the source said.
The U.S. official said Washington was willing "to support Turkey as an escrow location, providing the Iranian LEU [Low-Enriched Uranium] left Iran immediately and providing the IAEA put it under full safeguards and monitoring."
Turkish foreign ministry officials deny any phone conversation took place.
"There were some allegations that the minister talked to Mrs. Clinton but this did not happen," Selim Yenel, deputy undersecretary of Turkish Foreign Ministry, told CNN.
The offer -- announced in a joint statement Monday by Iran, Turkey and Brazil -- would have Iran send 1,200 kg (2,645 lbs) of its low-enriched uranium to Turkey within a month, and the international group monitoring Iran's nuclear activities send 120 kg (264 lbs) of high-enriched uranium to Iran within a year.
The group to whom Iran is making the offer -- the so-called Vienna Group of the United States, Russia, France, and the International Atomic Energy Agency -- did not respond immediately.
But the United Kingdom did not seem satisfied.
"Foreign Minister (Manouchehr) Mottaki told U.N. Security Council ambassadors last week that this enrichment would continue regardless of any deal to resupply the Tehran Research Reactor. There is no apparent civilian use for this material and it underlines Iran's disregard for efforts to engage it in serious negotiation," British Foreign Office minister Alistair Burt said in a statement Monday.
In France, Bernard Valero, a spokesman for Foreign Minister Bernard Kouchner, noted that "Iran (has) made several contradictory statements on this matter over the past few months."
Valero also said Iran "must put an immediate end" to "constant violations" of U.N. Security Council resolutions regarding its uranium-enrichment activities.
He said France needs time to examine Iran's position before commenting in detail on the latest developments.
An official in Israel said that country also was awaiting more details to determine whether the agreement is "another scheme by Iran to deceive the international community and play for time.
"In the past, they have already seemingly accepted a number of proposals only to recheck them at the last moment," said the Israeli official, who asked not to be named because of the sensitivity of the issue.
"So time will tell whether this is a breakthrough or, as seems more likely, a clever manipulation of Turkey and Brazil, taking advantage of Brazil's naivety, good faith and lack of experience in Middle East affairs," the official said.
Iran, Turkey and Brazil said Iran would formally notify the IAEA of the proposal within a week.
If the deal is not accepted, Turkey will return Iran's low-enriched uranium, the joint statement said.
Turkish foreign ministry spokesman Burak Ozugergin said Iran had made a major concession.
"Iran is ready to deliver," Ozugergin said. "If the deal goes through that's fine. If it doesn't, then the 1,200 kilograms in Turkey will continue to belong to Iran and can be arranged for return."
It is not clear how Iran's insistence that it will continue to enrich uranium itself is related to its offer to send low-enriched uranium abroad.
Tehran said it needs to enrich uranium from its current 3.5 percent to 20 percent because a research reactor that produces isotopes for cancer patients is running out of fuel.
But uranium enriched to 20 percent is the threshold for setting off a nuclear reaction. The United States and other Western nations have accused Tehran of trying to develop a nuclear weapons program, but Iran's government insists the material is for civilian use.
Western nations had been asking Iran to send the low-level uranium out of the country to be enriched elsewhere, but Tehran had resisted until now.
Iran reached its decision after a meeting with Turkish Prime Minister Recep Tayyip Erdogan and Brazilian President Luiz Inacio Lula da Silva.
The exchange will take place a month after Iran receives the official approval from the International Atomic Energy Agency, said foreign ministry spokesman Mehmanparast.
The five permanent U.N. Security Council members plus Germany offered Iran a deal: send the low-level uranium out of the country to be enriched elsewhere in exchange for fuel for its reactor.
Tehran did not accept but instead made a counteroffer: make the swap a simultaneous one and carry it out on Iranian soil.
The U.S. State Department called the Iranian proposal a stalling tactic and said world powers would not "front" the fuel to Iran.
A stalemate ensued.
The United States then sought support for expanded sanctions against Iran, saying Iran is unlikely to negotiate unless sanctions are in place.
Brazil and Turkey -- both temporary members of the security council -- had been working toward a diplomatic solution that does not involve sanctions.
CNN's Reza Sayah, Matthew Chance and Ivan Watson contributed to this report.