Iran said on Saturday it will enrich uranium, the most controversial part of its atomic programme, to the 20-percent purity required for a research reactor in Tehran if third-party deals fail.

Ali Shirzadian, spokesman of Iran Atomic Energy Organisation, said the UN atomic watchdog would be responsible if any third-party deal to process high grade uranium broke down.

He also expressed hope the United States would not "disturb" any such deal.

"We will write a letter and announce to the (International Atomic Energy Agency) agency that Iran will act directly to supply the fuel for the Tehran reactor," ISNA news agency quoted Shirzadian as saying when asked what would happen if proposed third-party deals fail.

Officials from Iran, the United States, Russia, France and the IAEA are to meet in Vienna on October 19 to work out the modalities for deals under which Tehran has said it is ready to buy 20 percent pure uranium from abroad.

"Iran fully owns the enrichment technology and therefore it will sit at the negotiating table with leverage," Shirzadian said, adding that Tehran prefers to "buy the fuel for the Tehran reactor in bulk as it is more economical."

He said the reactor needs around 200 kilogrammes (440 pounds) of 20 percent pure uranium to operate, but did not say how long that would last.

During recent talks in Geneva between Tehran and six major world powers, Iran agreed to buy the higher grade uranium required from overseas suppliers.

Uranium enrichment lies at the heart of Western concerns about the Iranian nuclear programme. The sensitive process can produce fuel for civilian nuclear reactors or, in highly extended form, the fissile core of an atomic bomb.

Western powers suspect Tehran's nuclear programme is aimed at making atomic weapons, a charge vociferously denied by Iran.

Global powers were outraged after Iran, just days ahead of the Geneva talks, revealed to the IAEA that it was building a second enrichment plant near the holy city of Qom.

During the talks Tehran agreed to open the facility for IAEA inspection and following last week's visit of Mohamed ElBaradei, chief of the agency, it was decided that UN inspectors would check the plant on October 25.

Soon after the revelation of the new facility, ElBaradei accused Iran of being on the "wrong side of the law" for having kept the building of the plant secret, a charge also denied by Iranian officials.

Shirzadian said Tehran will enter the Vienna talks and "if an agreement is arrived at and then not implemented for any reason, the agency and the country which broke it will be blamed."

"If the United States wants to disturb ... it is not a matter between Iran and the agency. It is a matter between the agency and the United States," Shirzadian added, suggesting that would be responsibility of the agency to tackle that issue and that Iran would proceed on its own for higher enrichment.

Ahmadinejad has previously indicated that Iran could even buy the 20 percent enriched uranium from US suppliers.

On Saturday, the state television website quoted him as saying that "the world must know that the Iranian nation ... will not back down an inch from its revolutionary ideals." It did not elaborate.

Iranian observers claim US officials have been taking strong initiatives toward resolving the crisis surrounding the Iran nuclear programme as seen from direct talks between Tehran and Washington's delegations during the Geneva talks.

US delegation head William Burns held direct talks with Iran's top nuclear negotiator Saeed Jalili, the first such talks since diplomatic ties between the two countries broke in the aftermath of the 1979 Islamic revolution.

The Iranian nuclear controversy is also expected to dominate US Secretary of State Hillary Clinton's trip to Europe and Russia starting on Saturday.

earlier related report
Iran warns against attack, boasts nuclear talks success
Iran issued another warning on Friday against any attack on the Islamic republic, while claiming its talks with world powers over its controversial nuclear programme were "a success and a victory."

Supreme leader Ayatollah Ali Khamenei's deputy representative to the elite Revolutionary Guards, Mojtaba Zolnour, said Tehran will "blow up the heart" of Israel if attacked by the Jewish state or the United States.

"Even if one American or Zionist missile hits our land, before the dust is settled, Iranian missiles will blow up the heart of Israel," state news agency IRNA quoted Zolnour as saying.

Iranian officials have repeatedly said Tehran would carry out severe reprisals if Israel or the United States attacked the country.

The United States and its regional ally Israel have never ruled out a military option to stop Tehran's nuclear drive, which the West says is aimed at making nuclear weapons while Iran says it is solely for peaceful ends.

After the 1979 Islamic revolution, Tehran withdrew its recognition of Israel.

The Jewish state considers the Islamic republic to be its arch-enemy after repeated statements by President Mahmoud Ahmadinejad that the Holocaust was a "myth" and that Israel is doomed to be "wiped off the map."

Another Khamenei appointee and one of Tehran's Friday prayer leaders, Ahmad Khatami, also issued a stern warning to Iran's enemies, without naming any.

"As our leader has said, our enemies are pursuing an Iranophobia scenario against us, and they are saying Iran is against world peace. But the world has understood that what they say is a lie," Khatami told worshippers in a sermon broadcast live on state-run radio.

"The enemy should know that if they want to hurt Iran they will receive such a slap that they will not be able to stand up," he added amid the habitual chants of "death to American and death to Israel."

Last month, Iran disclosed that it was building a second uranium enrichment plant, angering world powers and drawing an accusation from UN atomic watchdog chief Mohamed ElBaradei that having kept the work secret was on the "wrong side of the law."

Tensions increased only days later, and just days before crucial talks in Geneva with world powers over Tehran's controversial nuclear programme, when Tehran tested several short- and medium-range missiles.

Khatami labelled those talks a "success and victory."

"The Geneva talks were a success and a victory for the Islamic republic system (since) even the Zionist and world arrogances' media confirmed this," he said.

"We owe this success to the wise guidance of the supreme leader and the ninth and tenth governments following his guidance," he added in reference to Ahmadinejad's previous and current administrations.

Iranian officials have maintained that they had the upper hand in the negotiations, with Ahmadinejad on Wednesday calling them a "step forward."

Western governments have been seeking reassurances that Iran's nuclear programme is entirely peaceful, and Iran agreed to open the newly disclosed enrichment plant to UN inspection.

Soon after the talks, ElBaradei visited Tehran to work out the modalities of the inspection, which is due to take place on October 25.

Iran also offered to send low-enriched uranium abroad so that it could be enriched to higher levels by a third party, and is to meet with France, Russia and the United States in Vienna on October 19 to work out the modalities.

Uranium enrichment lies at the heart of Western concerns about the Iranian nuclear programme. The sensitive process can produce fuel for civilian nuclear reactors or, in highly extended form, the fissile core of an atomic bomb.