The "huge task" of disabling parts of Iran's nuclear infrastructure will probably start this week, a top official said Sunday as US President Barack Obama took steps to end sanctions.

Ali Akbar Salehi, head of Iran's nuclear agency, told state television he was awaiting President Hassan Rouhani's order to remove thousands of centrifuges from atomic sites at Natanz and Fordo.

The rendering of the centrifuges -- fast-spinning machines that enrich uranium -- was part of a July 14 deal, known as the Joint Comprehensive Plan of Action, between Iran and six world powers to end a 13-year dispute over Tehran's atomic activities.

On Sunday, Obama ordered the US government to "take all appropriate additional measures to ensure the prompt and effective implementation of the US commitments set forth in the JCPOA".

The US measures will take effect upon confirmation by Secretary of State John Kerry that Iran has met its commitments under the accord, Obama said, likely at the end of 2015 or early 2016.

As well as slashing its number of centrifuges to around 6,000, Iran will have to satisfy the International Atomic Energy Agency that it has taken steps to ensure its Arak reactor and other installations cannot be used for military purposes.

The IAEA's final report on Iran is due by December 15.

"We will start our actions when the president gives the order," Salehi said of Rouhani, estimating that the work to comply with the JCPOA would take around two months.

"What we need to accomplish is a huge task. We hope to start this week or next week."

The July agreement won final approval in Iran on Wednesday.

In Tehran, some hardline lawmakers say Rouhani's government made too many concessions to the West. The deal also came despite fierce opposition from US and Israeli critics who say safeguards on Iran are not sufficiently robust.

Iran has always denied seeking a nuclear weapon. The accord is meant to ensure it never can through an inspection regime over 15 years.