The European Union and the United States have suspended a range of sanctions against Iran after Tehran began implementing a deal to curb its nuclear programme.
The move eases restrictions on trade in petrochemicals and precious metals and on the provision of insurance for oil shipments, among other measures.
In the US, the Treasury Department said that now that Iran has fulfilled its initial nuclear commitments under the deal, "the administration has taken the necessary steps to pause efforts to further reduce Iranian crude oil exports".
An EU statement on Monday said the bloc had "suspended certain EU restrictive measures against Iran for a period of six months".
Earlier in the day, Iranian state media said the country had started to shut down its most sensitive nuclear work, as required under the deal.
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.
The West alleges that Iran is covertly using its nuclear programme to build a nuclear bomb. Tehran insists the programme is solely for peaceful purposes.
The historic deal reached in Geneva on November 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 on 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.
Under the Geneva deal, Iran agreed to halt its 20 percent enrichment programme 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 programme to greater UN inspections and providing more details on its nuclear activities and facilities.