UN nuclear monitors were heading to North Korea on Tuesday to discuss the communist nation's plans to fulfill its long-delayed pledge to shut down its main nuclear reactor. The North Korean government vowed Monday to move forward with a February agreement to shut down its plutonium-producing Yongbyon reactor in exchange for aid, after announcing that a dispute over frozen bank funds that had held up disarmament efforts was now finally over. South Korea responded Tuesday by saying it will start sending promised food aid to North Korea on June 30. The South agreed in April to give the impoverished North 400,000 tons of rice. But the delivery - originally set to begin in late May - was put on hold as Seoul used the food aid as leverage to spur the North to shutter Yongbyon. Officials from the International Atomic Energy Agency were heading from Beijing to the North Korean capital Tuesday for a five day visit. How to verify that Pyongyang is taking the reactor off-line will dominate their agenda, said the group's leader, Olli Heinonen. U.S. Assistant Secretary of State Christopher Hill said Saturday he believed the shutdown would happen within about three weeks. Hill is the top U.S. nuclear negotiator with the communist regime. However, Heinonen said it will be up to North Korea to decide how quickly the facility is shut and sealed. "They are the ones who (will) shut it down and not us so they have to make their own plans. How long it will take is a little bit up to them," Heinonen said in Beijing on Tuesday ahead of his departure for Pyongyang. "These are the details we are going to discuss now when we go there." He said Monday he was unsure whether he would have a chance to actually visit the Yongbyon site. Still, the visit fueled optimism that Pyongyang finally was ready to move forward with its disarmament commitments. North Korea, which expelled UN inspectors in late 2002, announced last week that it invited a "working-level delegation" to discuss procedures for shutting down the plutonium-producing facility. North Korea had pledged in February to shut down the Yongbyon reactor, its main processing facility, and IAEA Chief Mohamed ElBaradei traveled to North Korea in March in what was billed as a landmark visit. But Pyongyang refused to act on the promise until it received about US$25 million in funds that were frozen in a Macau bank amid a dispute with the U.S. over alleged money-laundering. On Monday, North Korea announced the banking dispute had been resolved. The North's Foreign Ministry said the disputed funds "have finally been transferred according to our demand," said a report from the North's official Korean Central News Agency. The ministry also said it would start implementing the February disarmament accord, in which it promised to shut down its nuclear reactor in exchange for economic and political concessions. U.S. officials have been saying since earlier this month that the financial obstacle had been overcome, but North Korea's statement Monday was the country's first confirmation that the money transfer was finished and the matter was fully wrapped up. South Korea's decision to start shipping food aid was made "in consideration of the request of the public and international community on a humanitarian issue," Unification Minister Lee Jae-joung said at a press conference. Pyongyang has relied on outside handouts to feed its 23 million people since its economy was devastated by natural disasters and mismanagement in the mid-1990s. Lee said that South Korea notified North Korea earlier in the day regarding the decision.