TEHRAN, Iran — Iran started to shut down its most sensitive nuclear work today, part of a landmark deal struck with world powers that ease international concerns over the country’s nuclear program and clearing the way for a partial lifting of sanctions, the state media said.

The United Nations nuclear agency, the International Atomic Energy Agency, confirmed that higher-level uranium enrichment in the Natanz facility in central Iran had been stopped.

Iran’s decision to halt higher-level enrichment is seen as a key step toward easing Western fears over Tehran’s nuclear program. The West fears Iran seeks to build a nuclear bomb. The Islamic Republic insists the program is solely for peaceful purposes.

The shutdown follows a historic deal Iran reached with world powers in Geneva on Nov. 24 that calls for an end to higher-level enrichment in exchange for the lifting of some economic sanctions.

Iranian state TV said authorities halted enrichment of uranium to 20 percent by disconnecting the cascades of centrifuges enriching uranium at the facility. That level is just steps away from bomb-making materials.

The broadcast said international inspectors were on hand to witness the stoppage before leaving to monitor the suspension of enrichment at Fordo, another uranium enrichment site in central Iran.

The official IRNA news agency said Iran also started today 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.

Under the Geneva deal, Iran agreed to halt its 20 percent enrichment program but continue enrichment up to 5 percent. It also agreed to convert half of its stockpile of 20 percent enriched uranium to oxide and dilute the remaining half to 5 percent over a period of six months.

In addition to the enrichment measures, the six-month interim deal also commits Iran to opening its nuclear program to greater U.N. inspections and providing more details on its nuclear activities and facilities. Iran will also refrain from commissioning its under-construction 40 megawatt heavy water reactor in Arak, central Iran.

The U.S., European Union and other world powers are studying the U.N. nuclear agency report, said U.S. State Department deputy spokeswoman Marie Harf.

In exchange, Iran receives a halt to new sanctions and easing of existing sanctions. Measures targeting petrochemical products, gold and other precious metals, the auto industry, passenger plane parts and services will be lifted immediately.

The Geneva deal allows Iran to continue exporting crude oil in its current level, which is about 1 million barrels a day.