It’s up to the International Atomic Energy Agency , headed by Yukiya Amano, to verify that Iran has fulfilled all its commitments under the landmark nuclear deal. REUTERS

Iran removed the core of its plutonium reactor and filled it with concrete Monday, paving the way for economic and financial sanctions to be lifted soon.

The work that effectively rendered the reactor at Arak harmless was the last major hurdle for Iran to fulfill its commitments under a landmark deal reached just shy of six months ago in Vienna. The International Atomic Energy Agency must verify that everything was done satisfactorily before U.S. and international sanctions can be lifted. But that is expected to take days, not weeks.

“In a few days, we will see the end of the cruel sanctions against Iran,” President Hassan Rouhani said in a speech in southern Iran. “When sanctions end, I will explain to people how great of an accomplishment this is.”

The lifting of sanctions will unlock Iran’s access to about $100 billion in its own assets that has been frozen in foreign banks. The United States and the United Nations have prepared the legal steps necessary for sanctions relief to take effect.

That should give Rouhani a significant political boost before parliamentary elections in late February. He won election in 2013 promising to end sanctions that have undercut the economy. He returned to that theme in his speech Monday, when he predicted the upcoming new year, which is marked in Iran in March, would be a one of “economic revival” despite oil prices slumping to an 11-year low.

Predictions of an imminent end to sanctions were echoed by European Union foreign policy chief Federica Mogherini, who said Monday in Prague that the implementation day of the Iran agreement “could come rather soon.” Last week, Secretary of State John F. Kerry said it was just “days away.”

The desire to get the money, which Iran desperately needs to rebuild creaky infrastructure and pay off debts, has propelled Tehran to move speedily in fulfilling the promises it made in Geneva in July. Just two weeks ago, it shipped out most of its stockpile of low-enriched uranium. It has dismantled thousands of uranium-enriching centrifuges and placed them into storage. Dismantling the Arak reactor, which would have produced enough plutonium to make two nuclear weapons a year, was the last major chore.

“In removing the core of the reactor, Iran has moved past the point of no return,” said Kelsey Davenport, director of nonproliferation policy at the Arms Control Association. “We’re on the brink of a historic accomplishment that limits Iran’s nuclear capabilities.”

The work has gone faster than U.S. officials predicted. When the agreement was reached last year, they estimated it would take Iran six to nine months and said sanctions would not be lifted before this spring. In part, they were making guesses on a process with limited precedent — the dismantling of a nuclear program. But they also underestimated Tehran’s determination to end sanctions.

“A key driver was the motivation of the Rouhani administration to get this done before the February elections,” said Robert Einhorn, a senior fellow at the Brookings Institution. “Clearly the administration wants to try to reap the electoral benefit of sanctions relief.”

Even as the deal’s implementation races forward, members of Congress have been urging President Obama to impose new sanctions on Iran related to ballistics missile tests it conducted in October and November. Iran has said that would violate and nullify the deal, and such legislation would probably be vetoed by Obama.

“I don’t think at this stage there’s anything Congress could do to derail ‘Implementation Day,’ ” Einhorn said.