TOKYO (AP) – North Korea could shut down its plutonium-producing reactor within three weeks, a top American nuclear envoy said Saturday after returning from a rare visit to the reclusive country.

Christopher Hill – the chief American negotiator at international talks on North Korea’s nuclear programs – also told reporters in Tokyo that the next round of nuclear negotiations could begin in early July, before a full shutdown of the Yongbyon reactor.

Mr. Hill said the reactor would be closed after North Korea and the U.N.’s nuclear watchdog agree on how to monitor the process. U.N. inspectors are to arrive in North Korea on Tuesday.

“We do expect this to be soon, probably within three weeks … though I don’t want to be pinned down on precisely the date,” Mr. Hill told reporters after briefing his Japanese counterpart, Kenichiro Sasae, on the outcome of his two-day surprise trip to the North Korean capital.

North Korea’s official Korean Central News Agency described the talks as “comprehensive and productive” on Saturday.

The trip – the first by a high-ranking American official since 2002 – came amid growing optimism that North Korea may finally be ready to take concrete steps toward fulfilling a promise to dismantle its nuclear programs.

Last week, the secretive nation invited inspectors from the International Atomic Energy Agency to begin discussing the procedures for shutting down its Yongbyon reactor. The country expelled the U.N. nuclear inspectors in late 2002.

The IAEA announced Friday that a delegation led by Olli Heinonen, the agency’s deputy director general for safeguards, would arrive in Pyongyang on Tuesday for a five-day visit.

Mr. Hill said earlier he was happy that the team was set to go, but cautioned that halting the reactor was just a first step.

“Shutting down the reactor won’t solve all our problems, but in order to solve our problems we need to make this beginning,” he told reporters after arriving in Tokyo. “We really think this is the time to pick up the pace.”

North Korean officials told Hill during his visit that they were prepared to shut down the Yongbyon facility as called for in a disarmament agreement reached in February, under which North Korea pledged to close the reactor and allow in U.N. inspectors in exchange for energy aid.

North Korea was to have done that by mid-April, but missed the deadline over a delay in resolving a separate financial dispute involving North Korean funds frozen at a Macau bank.

The bank was blacklisted by America for allegedly aiding North Korea in money laundering and counterfeiting, leading to the freezing of some $25 million of North Korean money.

The funds were freed earlier this year, but only last week started to be transferred to a North Korean account at a Russian bank.

Russian news agencies, citing unnamed finance ministry officials, reported Saturday that the North Korean funds had reached Dalkombank, a bank in the Russian Far Eastern city of Khabarovsk.

Bank officials could not be located to comment on the reports, while no one answered phones at the Central Bank or the Finance Ministry.

Russia’s deputy foreign minister said Friday the funds would be fully transferred sometime next week.

North Korea had made the money’s release a main condition for its disarmament, and used the financial dispute as a reason to stay away from six-party nuclear talks – involving the two Koreas, China, Japan, Russia and America – for more than a year, during which it conducted its first-ever nuclear test explosion in October.

Mr. Hill said Saturday that talks could begin before the reactor was fully shut down.

“I would expect it to happen soon after shutdown begins,” Hill said, adding the exact timing depended on scheduling by the host nation, China.

KCNA said that during Hill’s trip, “both sides shared the views that they would start implementing the (February) agreement on the premise that the issue of the remittance of the funds is finally settled.”

North Korea is to ultimately get aid worth 1 million tons of heavy fuel oil and other political concessions after it fully disables the reactor.

KCNA also said the two sides would seek to hold a meeting in early August of foreign ministers from the six nations in the nuclear talks on the sidelines of an Asian security forum in the Philippines.

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Associated Press writer Bo-Mi Lim in Seoul contributed to this report.