"We attach importance to and support this agreement," foreign ministry spokesman Ma Zhaoxu said.

"We hope this will help promote the peaceful settlement of the Iranian nuclear issue."

Iran's nuclear fuel exchange accord signed with Turkey and Brazil has "checkmated" US efforts to slap new sanctions on Tehran over its atomic programme, a government-owned newspaper said on Tuesday.

"America checkmated by Tehran three-way accord," said the daily Iran.

Columnists in the top reformist daily Shargh urged rival factions and government critics to back the deal, which it hoped would blunt efforts to impose further sanctions on Tehran.

"You can complain why they postponed a decision which could have been taken months ago but the new policy should be supported," prominent reformist analyst Abbas Abdi wrote.

Leading daily Kayhan hailed "Iran's intelligence and strength" and insisted Tehran would be the "winner" whether world powers rejected or accepted the deal.

But one conservative newspaper lashed out at the government.

"Despite the official propaganda, yesterday's accord is not a victory but backing down in the face of Western greed, and Iran should not submit to it," said an editorial in Jomhuri Eslami.

The accord signed on Monday with Brazil and Turkey commits Iran to deposit 1,200 kilograms (2,640 pounds) of low enriched uranium (LEU) in Turkey in return for higher grade fuel for a Tehran research reactor.

But the United States said moves for toughened sanctions would still go ahead.

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

Gibbs, who had earlier issued a written statement expressing "serious concerns" about the deal, said that if Tehran lived up to the new pact it would represent "some progress."

But even if that took place, Gibbs said Washington had concerns about the "overall thrust" of the nuclear programme and the fact Tehran said it would continue enriching uranium to 20 percent.

State Department spokesman Philip Crowley said: "There are those who might characterize this as a breakthrough. I think we remain skeptical that this represents anything fundamentally new."

However, he said US officials were still evaluating the accord, and planned to consult with its international partners in the coming days, including with Brazil and Turkey.

Turkish Foreign Minister Ahmed Davutoglu said there was "no need" for further UN sanctions in the light of the deal as his country and Brazil "have made guarantees and the low enriched uranium will remain in Turkey."

Brazilian President Luiz Inacio Lula da Silva, a driving force behind the accord, said: "Diplomacy emerged victorious today. It showed that it is possible to build peace and development with dialogue."

Monday's signing came after three-way talks in Tehran by President Mahmoud Ahmadinejad, Lula and Turkish Prime Minister Recep Tayyip Erdogan.

Lula and Erdogan are due to meet again on Tuesday in Madrid on the sidelines of the EU-Latin America summit, according to the Brazilian president's agenda.

EU foreign affairs chief Catherine Ashton said Monday's accord only "partly" responds to the demands of the International Atomic Energy Agency (IAEA), which has been probing Iran's nuclear programme for years.

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 line with what was stated there, we are now expecting written notification from Iran that it agrees with the relevant provisions included in the declaration," said spokeswoman Gill Tudor.

Ashton said an IAEA offer in October for Iran to have its uranium enriched abroad recognised the right for civil nuclear power, but was "not an attempt to address the underlying issue... which is the nuclear weapon intention issue."

Russian President Dmitry Medvedev had previously welcomed the agreement but said further talks were needed.

"What was done by our colleagues needs to be welcomed. This is the politics of a diplomatic solution," he said. "We need to have consultations with all the parties, including Iran, and then determine what to do next."

Iran had said the signing meant the ball was now in the court of Western powers, and Ahmadinejad called for fresh talks over Tehran's nuclear programme.

"I hope the 5+1 (UN Security Council permanent members plus Germany) enter talks with honesty, respect and fairness and heed the great work started in Tehran," the official IRNA news agency quoted him as saying.

Britain expressed reservations. "Iran's actions remain a serious cause for concern," junior foreign minister Alistair Burt said.

Germany said nothing could replace the IAEA deal that envisages Iran's 3.5 percent LEU being sent to Russia and France for enrichment to 20 percent and then returned as fuel for the Tehran reactor.

The UN-brokered offer appeared to be a breakthrough in long-stalled discussions over the refueling of the Tehran research reactor that makes radioisotopes for cancer treatment.

But Iran has so far stalled on the deal the IAEA has been trying to persuade it to sign since October, insisting it wants to keep the uranium on its own soil for a simultaneous swap with reactor fuel.

Under the new agreement, Tehran is ready to deposit more than half of its LEU in Turkey "within one month."

In return, the United States, France and Russia would deliver 120 kilos of fuel needed for the reactor "in no later than one year."

Israel -- the sole if undeclared nuclear-armed power in the Middle East -- was quick to accuse Tehran of manipulating Turkey and Brazil and seeking to buy time in the long-running nuclear standoff.

Israeli Prime Minister Benjamin Netanyahu was to meet on Tuesday with senior members of his cabinet to formulate Israel's response to the Iran-Turkey nuclear deal, officials said.

"The prime minister is holding security consultations," a senior Israeli official said, speaking on condition of anonymity.

Late on Monday, Netanyahu ordered his ministers not to discuss the issue until Israel issues a formal response, his office said.

Middle East Online