The measures will take effect upon confirmation by the Secretary of State that Iran has met its commitments under the so-called Joint Comprehensive Plan of Action (JCPOA), as the accord is known, Obama said.

President Barack Obama ordered the U.S. government Sunday to take steps towards lifting sanctions on Iran, in accordance with the historic nuclear deal struck between six world powers and Tehran.

Obamas directive comes 90 days after the U.N. Security Council endorsed the accord signed in Vienna in July, a milestone referred to as “Adoption Day.”

“I hereby direct you to take all necessary steps to give effect to the U.S. commitments with respect to sanctions,” Obama said in a memorandum addressed to the U.S. secretaries of state, energy, commerce and the treasury.

The measures will take effect upon confirmation by the Secretary of State that Iran has met its commitments under the so-called Joint Comprehensive Plan of Action (JCPOA), as the accord is known, Obama said.

“This is an important day for all of us and a critical first step in the process of ensuring that Iran’s nuclear program will be exclusively for peaceful purposes,” Secretary of State John Kerry added in a statement.

But no sanctions will be lifted immediately – full relief will come not on “adoption day” but on “implementation day,” the point when the IAEA is able to certify that Iran has fully complied with its end of the bargain.

Under the deal with world powers, Iran will dramatically reduce its uranium enrichment program, surrender or dilute most of its highly enriched fuel and open its nuclear sites to inspectors from the IAEA, the U.N. nuclear watchdog.

A top official said Sunday the “huge task” of disabling parts of Iran’s nuclear infrastructure would probably start this week, as Obama was taking steps to end the sanctions.

In return, the United States, Europe and other countries will rescind a raft of economic sanctions imposed on Iran because of fears that its nuclear research program concealed plans to develop an atomic bomb.

Tehran has said it hopes “implementation day” will come quickly, in less than two months, but Washington envisages a longer timeframe.

“For us it’s important that it’s done right, not that it’s done quickly,” a senior administration official told reporters. “We cannot imagine less than two months.”

Ali Akbar Salehi, head of Iran’s nuclear agency, told state television he was awaiting President Hassan Rowhani’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.

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 Dec. 15.

“We will start our actions when the president gives the order,” Salehi said of Rowhani, 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.

Also on Sunday the European Union published legal acts that would open the way for the bloc to lift sanctions if Tehran met the conditions tied to a landmark nuclear agreement between Iran and world powers.

The legal acts would have no immediate effect, but would cement the process.

“The EU today adopted the legislative framework for lifting all of its nuclear-related economic and financial sanctions,” EU High Representative for Foreign Affairs Federica Mogherini and Iranian Foreign Minister Javad Zarif said in a joint statement.

“It will take effect on Implementation Day, simultaneously with the IAEA-verified implementation of agreed nuclear measures by Iran,” the statement said.

In Tehran, some hardline lawmakers say Rowhani’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.

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