North Korea confirmed it has shut its nuclear reactor that provides the secretive state with material to make weapons-grade plutonium, Xinhua quoted a North Korean official as saying on Sunday.

North Korea told the United States it has shut down its Soviet-era Yongbyon reactor as part of a disarmament deal, the US State Department said on Saturday after a team of UN nuclear inspectors arrived in Pyongyang.

“We have shut down the nuclear facilities at Yongbyon after we received the first shipment of heavy oil,” the North’s KCNA news agency cited one of its spokesman as saying, according to Xinhua.

State Department spokesman Sean McCormack said in Washington that US negotiators looked forward to the next step of the February 13 agreement, in which Pyongyang “has committed to declaring all its nuclear programmes and disabling all its existing nuclear facilities”.

Top US nuclear envoy Christopher Hill gave the news a cautious welcome on Sunday. “This is just a first step,” Hill, who is visiting Japan, told Japanese media. “This is only a meaningful step insofar as it will be followed by other steps.”

South Korea’s Foreign Ministry hailed Pyongyang’s decision as an encouraging development. “North Korea’s measures to shut down the Yongbyon nuclear reactor and accept the IAEA inspectors are meaningful because it is the first step in implementing their denuclearisation agreement,” a ministry statement said.

Word of the reactor shutdown came on the day the IAEA team reached Pyongyang.