SEOUL, South Korea - North Korea loaded booster rockets onto a launch pad and moved about 10 fuel tanks to a launch site in preparation to test-fire a long-range missile that could reach as far as the U.S. mainland, a newspaper reported Saturday. South Korea and the United States made the assessment after analyzing satellite images over the past few days, the Chosun Ilbo reported, citing an unnamed high-level South Korean government official. Also Saturday, the Japanese daily, Sankei Shimbun, reported that the missile launch could take place as early as Sunday. South Korean Foreign Ministry spokesman Choo Kyu-ho couldn't confirm the report. U.S. warnings The report follows warnings by the U.S. government that the communist state was accelerating preparations for testing a missile that has the potential to strike the United States. A U.S. government official said Friday that a test of the Taepodong-2 long-range missile may be imminent. The Washington official agreed to speak but only on the condition of anonymity because of the sensitivity of the information. State Department spokesman Sean McCormack told reporters Friday that any missile launch by the North Koreans would be a provocation and would violate their 1999 moratorium on long-range missile tests. The Taepodong-2 is a three-stage missile, but the warhead section hasn't been loaded yet, the paper said. It said about 10 large tanks of liquid fuel have been moved to the site, but it wasn't clear if the fuel had been unloaded. The North's missile program has been a major security concern in the region, adding to worries about its pursuit of nuclear bombs. North Korea sent shock waves through the region when it test-fired a ballistic missile over northern Japan in 1998. Violation of declaration On Friday, Japan's Chief Cabinet Secretary Shinzo Abe said a launch would threaten Japanese security. "If North Korea launches the reported ballistic missile, which will directly affect Japan's security, it would be a violation of the Japan-Pyongyang Declaration," Abe said. The declaration was signed in 2002 at a Japan-North Korea summit in Pyongyang, and reaffirmed by the two nations in 2004, he said. South Korea said earlier this week that it conveyed "grave concern" to North Korea last month when signs first emerged that the North was preparing to test-fire a missile. North Korea has been under a self-imposed moratorium on long-range missile tests since 1999. Still, it has since test-fired short-range missiles many times, including two in March. The reports of a possible launch come after a prolonged hiatus in six-party nuclear disarmament talks designed to create a Korean Peninsula free of nuclear weapons. Persistent efforts by the United States and other members of the group to persuade North Korea to resume the discussions have not been successful. There have been no discussions since November. North Korea is demanding that the United States revoke sanctions that Washington imposed several months ago in response to alleged North Korean counterfeiting of U.S. dollars and other currency violations.