Scepticism greeted Iran's agreement on Monday to ship low enriched uranium to Turkey, with the United States saying it will not halt its quest for tough new sanctions.

"It does not change the steps that we are taking to hold Iran responsible for its obligations, including sanctions," said White House spokesman Robert Gibbs in Washington.

Iran earlier signed an agreement with non-permanent UN Security Council members Turkey and Brazil to ship 1,200 kilograms (2,640 pounds) of its low enriched uranium to Turkey for a later swap for fuel for a research reactor.

Gibbs -- who had earlier Monday issued a written statement expressing "serious concerns" about the deal -- said that if Tehran keeps its word, it would represent "some progress."

But even if that happens, he added, Washington has concerns about the "overall thrust" of Iran's nuclear programme and the fact that Tehran says it would keep enriching uranium to 20 percent.

EU foreign policy chief Catherine Ashton said Monday's deal failed to address the core issue, "which is the nuclear weapon intention issue."

Ashton, talking to reporters in Madrid where she was attending an EU-Latin America summit, said she would wait to see if Iran makes a move to resume talks with the West about its nuclear program.

"If they do, we will discuss it, if not we will continue what we are doing," she said.

In Paris, French foreign ministry spokesman Bernard Valero said: "Let's not be duped by this. A solution for the medical reactor, while necessary, would in no way resolve the problem posed by the Iranian nuclear program."

"The exchange of uranium that is envisaged amounts to a confidence gesture, a side issue," Valero told reporters.

His boss, Foreign Minister Bernard Kouchner, said the International Atomic Energy Agency (IAEA) must be the first body to respond to Monday's deal -- a position shared by Germany.

"It of course remains important that Iran and the IAEA reach an accord," its deputy government spokesman Christoph Steegmans said. "That cannot be replaced by an accord with other countries."

In Vienna, the IAEA said it had received the text of the joint declaration by Iran, Brazil and Turkey, but was now expecting Tehran to notify it directly of what commitments it had undertaken.

In London, British junior foreign minister Alistair Burt said: "Iran's actions remain a serious cause for concern, in particular its refusal to meet for discussions of its nuclear program, or cooperate fully with the IAEA."

Western diplomats close to the Vienna-based IAEA said the deal did not remove the case for further UN sanctions against Tehran, because Iran had to do more than just accept what amounted to a confidence-building agreement.

Russia, which has been reluctant to pursue new sanctions against Iran, was more optimistic.

"What was done by our colleagues needs to be welcomed. This is the politics of a diplomatic solution to the Iran problem," President Dmitry Medvedev told reporters during a visit to Kiev.

"We need to have consultations with all the parties, including Iran and then determine what to do next."

For the Israelis, who consider Iran's nuclear drive to be a major threat to their security, Tehran had succeeded in having "manipulated Turkey and Brazil," a senior Israeli official told AFP on condition of anonymity.

"The Iranians have already pulled off such a trick in the past -- by pretending to accept such a procedure to lower tensions and reduce the risk of harsher international sanctions, then refusing to follow through," he said.

But Brazil's President Luiz Inacio Lula da Silva called the deal a "victory for diplomacy."

US State Department spokesman Philip Crowley said the United States will be "consulting broadly in the coming days," including probably with Turkey and Brazil, to determine how to react to the document.

Although US officials are still evaluating the declaration, "we remain skeptical that this represents anything fundamentally new," Crowley said.

For example, he said, the document shows Iran still refusing to cede to the IAEA control of both the exported uranium and subsequent upgraded fuel transfer to the research reactor -- a "caveat" that proved a deal breaker in the past.