TEHRAN — Iran has started decommissioning the first of thousands of centrifuges used for enriching uranium as part of its commitments under the nuclear deal reached with global powers, the head of Iran’s nuclear energy program was quoted as saying on a visit to Japan on Monday.

The head of the Atomic Energy Organization of Iran, Ali Akbar Salehi, told the Kyodo News agency that Iran had started preliminary work, referring to centrifuges and other steps.

The entire process will “take some time,” said Mr. Salehi, who is also a vice president, a former foreign minister and a member of the nuclear negotiating team.