Story highlights U.S. and EU suspend some sanctions for 6 months

All voluntary steps will be done by Monday evening, Iran says

Iran struck the deal in November in exchange for lighter sanctions from Western powers

State media: Iran starts eliminating its stockpile of higher levels of enriched uranium

Iran started suspending high levels of uranium enrichment Monday as an interim deal struck with six world powers went into effect, state media reported, making way for more talks and fewer sanctions.

All of its voluntary moves will be completed by Monday evening, Iran's nuclear spokesman Behrouz Kamalvandi told state-run news agency IRNA.

The United States and European Union announced that they were suspending certain sanctions for six months as part of the deal.

"In reciprocation for Iran's concrete actions, the United States and its P5+1 partners -- the United Kingdom, France, Germany, Russia, and China -- as well as the European Union will today follow through on our commitment to begin to provide the modest relief agreed to with Iran," said White House spokesman Jay Carney. "At the same time, we will continue our aggressive enforcement of the sanctions measures that will remain in place throughout this six-month period."

Iran stopped enrichment of uranium to the 20% purity level and disconnected cascades of centrifuges enriching uranium in Natanz, a top nuclear official told state-run Press TV.

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A centrifuge is a mechanism used to enrich uranium.

"From now on, the centrifuges which were used for producing 20% enriched uranium will be used for enriching uranium to the 5% purity level," said Mohammad Amiri, a director in the nation's nuclear agency.

International inspectors were present when Iran started implementing the historic deal, Press TV said.

The action is part of a six-month interim agreement that gives Iran and the other countries more time to negotiate a permanent solution.

Iran struck the deal on November 24 in exchange for lighter sanctions.

Tehran insists its nuclear program is for peaceful, civilian energy purposes, despite concerns from the West that it's a guise for working toward a nuclear weapons program.

Nuclear power plants use uranium that is enriched to 5% as fuel to generate electricity.

As part of the agreement, Iran must eliminate its stockpile of higher levels of enriched uranium, dismantle some infrastructure that makes enrichment possible, and allow broader and more intrusive inspections of its programs.

The six nations and the European Union are reviewing a report by the U.N. watchdog, the International Atomic Energy Agency, which provided details of the nuclear activities on the first day of the deal, according to the U.S. State Department.

"This is an important day in our pursuit of ensuring that Iran has an exclusively peaceful nuclear program," said Catherine Ashton, the European Union foreign policy chief.

She said she's optimistic a new round of negotiations could come soon.

"Depending on how things work out today, I hope that we will start talks in the next few weeks," Ashton said.

If all conditions are met, Iran will get sanctions relief totaling about $7 billion, including access to $4.2 billion in frozen assets, during the six months the interim deal is in effect.

"The psychological effects of the lifting of sanctions will create a new atmosphere in the country," said Iran's Deputy Foreign Minister Seyed Abbas Araghchi, according to IRNA.

For years, Iran and Western powers have left negotiating tables in disagreement, frustration and open animosity.

The diplomatic tone changed last year when Iranian President Hassan Rouhani was elected.

And the deal appeared to be on the right track Monday.

As part of the deal, Iran was required to dilute its stockpile of uranium that had been enriched to 20%.

While uranium isn't bomb-grade until it's enriched to 90% purity, "once you're at 20%, you're about 80% of the way there," said Mark Hibbs, a nuclear policy expert at the Carnegie Endowment for International Peace.

The deal also mandates Iran halt all enrichment above 5% and dismantle the technical equipment required to do that.

World leaders applauded the interim deal after years of a stalemate.

"For the first time in nearly a decade, we have halted the progress of the Iranian nuclear program," U.S. President Barack Obama said when the deal was announced in November.