TEHRAN (AP) ― Iran unplugged banks of centrifuges involved in its most sensitive uranium enrichment work on Monday, prompting the United States and European Union to partially lift economic sanctions as a landmark deal aimed at easing concerns over Iran’s nuclear program went into effect.

The mutual actions ― curbing atomic work in exchange for some sanctions relief ― start a six-month clock for Tehran and the world powers to negotiate a final accord that the Obama administration and its European allies say will be intended to ensure Iran cannot build a nuclear weapon.

In the meantime, the interim deal puts limits on Iran’s program ― though it continues low levels of uranium enrichment. Tehran denies its nuclear program is intended to produce a bomb.

The payoff to Iran is an injection of billions of dollars into its crippled economy over the next six months from the suspension of some sanctions ― though other sanctions remain in place.

In part a reflection of a thaw between Washington and Tehran, the moves coincidentally occurred on the 33rd anniversary of the end of the Iran hostage crisis. The holding of 52 Americans for 444 days by radical Iranian students that ended Jan. 20, 1981, was followed by more than decades of U.S.-Iranian enmity that only began to ease last year with signs that Iran was ready to meet U.S. demands and scale back its nuclear activities.

British Foreign Secretary William Hague called the deal “an important milestone” ― but not the ultimate goal.

“It’s important that other sanctions are maintained and the pressure is maintained for a comprehensive and final settlement on the Iranian nuclear issue,” Hague said.

The Europeans are aiming to start negotiations on a final deal in February, though no date or venue has been agreed on yet. Iranian Foreign Minister Mohammad Javad Zarif said Saturday that Tehran is ready to enter talks as soon as the interim deal goes into force.

In the first step of the interim accord, Iranian state TV said authorities disconnected cascades of centrifuges producing 20 percent enriched uranium at the Natanz facility in central Iran. The broadcast said international inspectors were on hand to witness the stoppage before leaving to monitor suspension of enrichment at Fordo, another site in central Iran.

Iran also started Monday to convert part of its stockpile of 20 percent enriched uranium to oxide, which can be used to produce nuclear fuel but is difficult to reconvert for weapons use, the official IRNA news agency said.

After receiving independent confirmation of the steps from the United Nations watchdog, the International Atomic Energy Agency, EU foreign ministers in Brussels approved the partial sanctions suspension.

The White House also announced the suspension of some American sanctions on Iran.