The United States expects North Korea (search) to shut down its plutonium (search)-producing reactor within three weeks, a top U.S. nuclear envoy said Saturday, after returning from a rare visit to the reclusive state.

Christopher Hill (search) — the chief U.S. 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.

Hill said the reactor would be shutdown after the North and the U.N.'s nuclear watchdog agree on how to monitor the process. U.N. inspectors were expected to arrive in the North on Tuesday to discuss the shutdown.

"We do expect this to be soon, but probably within three weeks ... though I don't want to be pinned down on precisely the date," Hill told reporters after briefing his Japanese counterpart 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 U.S. official since October 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 state invited inspectors from the International Atomic Energy Agency to begin discussions on 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, a deputy director general of the IAEA, would travel to Pyongyang on Tuesday to prepare for the first inspection.

Hill said earlier he was "happy" that the team was set to go, but cautioned that shutting 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 on arriving in Tokyo. "We really think this is the time to pick up the pace."

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

Pyongyang 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 the U.S. 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.

Russia's deputy foreign minister later Friday said the funds will 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 the U.S. — for more than a year, during which it conducted its first-ever nuclear test explosion in October.

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 when it disables the reactor.

KCNA also said the two sides would cooperate to resume six-nation nuclear talks in early July, and a meeting of foreign ministers of those countries in early August.