TEHRAN: 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.

"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 Ali 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 throw 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 facility 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."

He also hoped the United States will not "disturb" any third-party deal.

"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.