SEOUL (AFP) - North Korea has started to reassemble its main nuclear facility, making good on threats after the United States failed to remove the communist state from a terrorism blacklist, reports said Wednesday. A South Korean Foreign Ministry source was quoted as saying restoration work at the Yongbyon complex began earlier in the day. The source, quoted by Yonhap news agency, said the information came from the United States, which received a report from the International Atomic Energy Agency. Japan's Kyodo News and US cable television network Fox News carried similar reports. Kyodo, quoting diplomats in Beijing, said North Korea began the work on Tuesday. South Korean Foreign Ministry officials could not immediately be reached for comment. "We don't know anything about it," Japan's top government spokesman Nobutaka Machimura told reporters in Tokyo. North Korea last November began disabling its plutonium-producing reactor and other plants at Yongbyon under US supervision as part of a six-nation disarmament-for-aid deal. But on August 26 it announced that it had stopped disabling its nuclear plants and would consider restoring them in protest at the US refusal to remove it from the terror blacklist. The United States says the North must accept strict procedures to verify a declaration it made in June of its nuclear activities before it can be taken off the blacklist, which blocks US economic aid and some multilateral assistance. Fox News quoted unidentified US officials as saying the North's latest action is seen as a "symbolic gesture" because so much disablement work on the 20-year-old reactor has already been done. The North says 80 per cent of the disablement has been completed. Robert Einhorn, a former top State Department non-proliferation expert, said recently that the North Koreans were unlikely to resurrect the reactor, which was at the end of its lifespan. Daniel Pinkston, senior analyst with the International Crisis Group, told AFP it would probably take two years to put Yongbyon back into operation.