(Adds comments by U.S. official, paragraphs 16-17)

By James Vicini

WASHINGTON, July 14 (Reuters) - North Korea has told the United States it has shut down a nuclear reactor as part of a disarmament deal, the U.S. State Department said on Saturday after a team of U.N. nuclear inspectors arrived in Pyongyang.

"We welcome this development and look forward to the verification and monitoring of this shutdown by the International Atomic Energy Agency team that has arrived" in North Korea, State Department spokesman Sean McCormack said.

North Korea said last week it would consider suspending the operation of its nuclear facilities as soon as it received the first shipment of oil from South Korea under a Feb. 13 aid-for-disarmament deal.

A South Korean tanker carrying 6,200 tonnes of fuel oil arrived early on Saturday at the North Korea's northeastern port of Sonbong, the Unification Ministry in Seoul said.

McCormack said U.S. negotiators looked forward to the next step of the Feb. 13 agreement, in which North Korea "has committed to declaring all its nuclear programs and disabling all its existing nuclear facilities."

North Korea conducted its first nuclear test in October 2006.

The announcement about the shutdown of the Yongbyon nuclear facilities, made in a two-paragraph statement, came on the same day as the arrival in Pyongyang of a team from the U.N. nuclear watchdog agency.

The leader of the IAEA team said earlier in Beijing they would be go straight to Yongbyon, which is north of Pyongyang, on Saturday to begin work at the complex, which produces weapons-grade plutonium.

The team of 10 experts is the first to return to monitor the shutdown after a 4 1/2-year absence.

'GOOD STEP IN THE RIGHT DIRECTION'

IAEA Director General Mohamed ElBaradei has said it would take about a month to set up the monitoring equipment. "I am quite optimistic that this is a good step in the right direction," he said.

In his statement, McCormack said, "We, along with all our other six-party partners, remain firmly committed to achieving the denuclearization of the Korean Peninsula."

The six-party talks are scheduled to resume in Beijing on Wednesday, he said.

The talks, at which North Korea sits down with the United States, South Korea, China, Japan and Russia, are expected to map out the next stage of the disarmament process.

The other five have promised massive economic aid and better diplomatic ties if North Korea scraps its nuclear arms program.

"How smoothly the rest of the operation will go very much depends on how progress will be made in the six-party talks," ElBaradei said. "It is going to be a long process."

U.S. nuclear negotiator Christopher Hill, who is visiting Japan, told Japanese media he expects North Korea will produce a list of all its nuclear facilities in the coming weeks or months.

"We would expect the comprehensive list, declaration (of North Korea's nuclear programs) to be in a matter of several weeks, possibly couple of months," Hill said, according to a Kyodo report from the resort town of Hakone.

In 2002, the United States accused North Korea of operating a covert uranium enrichment program in violation of a 1994 nuclear-freeze deal. In December 2002, the North expelled IAEA inspectors and said it would restart its reactor. (Additional reporting by Jack Kim in Seoul, Chris Buckley and Lucy Hornby in Beijing and Chisa Fujioka in Tokyo)

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