Nuclear deal on Iran program to be implemented this year, says Iranian official

"Hopefully before the end of this year certainly we would have the implementation day," Araqchi told reporters after meeting senior officials from the United States, Russia, China, Britain, Germany and France in Vienna.

The United States and the European Union took formal legal steps on Sunday that will lift sanctions once Iran meets certain conditions such as reducing the number of centrifuges used to enrich uranium, and its enriched uranium stockpile.

Germany's foreign minister said the EU sanctions were likely to remain in place at least until January.

When asked whether Iran had started mothballing centrifuges, Araqchi said the process had not begun yet.

"We need an order by the president to the Iranian Atomic Energy Organisation to start the job. That would be done after some preparations that we still need to do in the coming days. So it would soon start," Araqchi said.

Sunday's moves have no immediate effect but cement a process that began with the deal reached in July to end sanctions against Iran once it shrinks its nuclear program.

In July Iran also agreed to reduce its stockpile of low-enriched uranium (LEU) to 300 kg of 3.67-percent fissile purification for 15 years. Weapons grade uranium must be enriched to around 90 percent fissile purity.

Iran's stockpile of uranium enriched to under 5 percent purity stood at 7,845.4 kg, according to the latest report by the U.N. nuclear watchdog.

Iran could dilute the excess LEU or sell it abroad in exchange for natural uranium.

"We are on schedule and we think we can do this business instead of diluting. We can do the business and receive natural uranium in return for selling our enriched uranium to outside," Araqchi said, declining to say whom Iran is in talks with.

Russia has in the past supplied Iran with reactor fuel.