A bitter rift between the world's top powers led by the United States and emerging nations Brazil and Turkey widened Thursday as differences over how to tackle Iran's suspect nuclear program erupted into sharp exchanges.

Turkey accused critics of a deal brokered with Iran last week for a nuclear fuel swap of being "envious" of the "diplomatic success" it represented -- in an implicit swipe at the United States.

US Secretary of State Hillary Clinton acknowledged "very serious disagreements" with Brazil over its insistence that the deal it helped to draw up be considered before a US push for new UN sanctions against Iran is decided.

The row threatens to split the UN Security Council, on which the United States sits as a permanent, veto-wielding member alongside temporary members Brazil and Turkey.

It also highlighted the growing assertiveness of Brazil, Latin America's biggest economy, and NATO member Turkey in carving out their own diplomatic tracks independently of the United States.

The United States accuses Iran of trying to build nuclear weapons under the cover of its atomic energy program, something Tehran denies.

Turkish Prime Minister Recep Tayyip Erdogan, speaking in a joint media conference in Brasilia with Brazilian President Luiz Inacio Lula da Silva, slammed detractors of the May 17 deal they worked out with Tehran.

"The countries criticizing this accord are envious. Because Brazil and Turkey brokered and pulled off a diplomatic success that other countries had been negotiating without result for many years," he said.

He stated that Brazil and Turkey had "assumed the responsibility" that went with their seats on the UN Security Council.

Lula urged that the UN nuclear watchdog, which this week received details from Tehran of the Brazil-Turkey proposal, to show "sensitivity in understanding the political moment" represented by the deal and to analyze it accordingly.

"Turkey and Brazil are working for peace. Up to now, Iran has met the obligations of its accord with Turkey and Brazil," he stressed.

Their words showed a stubborn refusal to allow the United States to dismiss their deal in its rush to secure a fourth round of sanctions against Iran in the UN Security Council.

US officials say they already have the backing of the four other permanent members -- allies France and Britain, as well as Iran's investment partners China and Russia -- and were confident they would win the nine votes needed on the 15-seat Security Council to impose the sanctions.

Non-permanent members Brazil and Turkey are opposed, along with Lebanon, which has ties to Iran through its Hezbollah militia.

Brazil was being especially fierce in fighting to save the Tehran fuel swap deal, both in official declarations and in what appeared to be a leak of a letter from US President Barack Obama to Lula ahead of negotiations over the accord.

The daily Folha de Sao Paulo reported Thursday that Obama had sent a letter to Lula three weeks ago suggesting negotiation points with Tehran and stating that he "would keep a door open to a compromise with Iran."

The letter reportedly also said Obama warned he would simultaneously push forward with the UN resolution for sanctions against Tehran.

The Brazilian government has not officially confirmed the authenticity of the letter, but Lula has insisted that the Tehran deal largely addressed the demands made by the United States months ago.

Under the terms of the deal, Iran would deposit around half its stock of low-enriched uranium in Turkey in exchange, within a year later, for reactor fuel enriched to a level needed for research and medical use -- but well below the level required for military ends.

The United States and its European allies say the deal is insufficient, partly because the amount of uranium to be handed over is too little, but mainly because Iran insists on enriching part of its remaining stock to 20 percent anyway.

UN chief Ban Ki-moon, speaking at the opening Thursday of a UN "Alliance of Civilizations" conference in Rio aimed at better cross-cultural understanding.

"This crisis, it seems to me that there is a serious lack of optimism and trust towards Iran in its core," he said.

He said Iran's plans to enrich its uranium "has caused serious concern" and stated: "It would be helpful if Iran agreed to stop trying to enrich uranium at 20 percent."

Without mentioning the US-led push for sanctions, Ban praised Lula and Erdogan's efforts "to resolve this issue with peaceful negotiation."

He acknowledged, though, that "there are different opinions about the approaches and possibilities concerning this issue."

earlier related report
Turkey chides US in Iran row, urges support for swap deal
Ankara (AFP) May 27, 2010 - Turkey insisted Thursday that rejecting a nuclear swap deal with Iran would be unreasonable and said that a US push for fresh sanctions on Tehran was creating an "absurd situation."

The swap deal, brokered by Turkey and Brazil last week, does not amount to a thorough solution of the Iran nuclear standoff "but it is a step forward on resolving the swap issue, which is one of the important elements of the nuclear file," foreign ministry spokesman Burak Ozugergin told reporters.

"It is true that the glass is half empty... but we say that further action should be now taken to fill itm," he added.

"It is unreasonable to reject the deal saying the glass is half empty."

The spokesman criticised the stance of the United States, which submitted a draft resolution at the UN Security Council for tough new sanctions on Tehran, shortly after Iran, Brazil and Turkey announced the deal.

"Submitting the paper a day after the agreement was reached means that you prefer to turn a blind eye to certain developments... This leads to an absurd situation," Ozugergin said.

The accord calls for Tehran to ship around half its stock of low-enriched uranium to Turkey and months later receive a supply of more highly-enriched uranium suitable for research and medical use.

The International Atomic Energy Agency (IAEA) said Monday it had received Iran's formal notification of the deal and would communicate the contents of the letter to the United States, France and Russia.

Western powers have been dismissive of the deal, arguing that it fails to allay key concerns about Tehran's uranium enrichment operations and that the international community should keep up the pressure on Iran.

"If suspicions persist on enrichment... the parties should sit down and talk," Ozugergin said.

"We are telling them to put the (swap) deal in their pockets and go on" talking.

He also hit back at criticism that the deal was technically flawed, notably suggestions that it failed to allocate enough time to produce the enriched uranium Iran would receive.

"We had contacts with Iran for the past eight or nine months... and we shared with third countries the main parameters of the talks. Is it now that they realise the fuel cannot be made within a year?" he said.

"There was time for technical considerations before Iran accepted the deal, but nothing much was said... Now it is our right, and Iran's also, to expect the other side to show good will and give an appropriate response," he said.

Turkey and Brazil, both non-permanent members of the Security Council, are opposed to fresh sanctions on Iran.

"We believe that a ground has been found to give further chance to negotiations," Ozugergin said.

Ankara's Islamist-rooted government, in power since 2002, has notably improved ties with Tehran, prompting discomfort in Israel, once a top regional friend, and raising eyebrows among Turkey's NATO allies.