North Korea has reportedly moved a ballistic missile capable of reaching the United States to a launching site, but officials in Seoul and Tokyo said they saw no reliable signs that the North intended to test the missile soon. Such a test would aggravate Pyongyang's relations with Japan and the United States, among others. Experts said that North Korean long-range missiles could deliver small warheads containing chemical and biological weapons, but that the North had not yet mastered the technology to fit its missiles with nuclear warheads. North Korea last tested a ballistic missile in 1998. Although analysts in the region doubt that Pyongyang would risk economic sanctions and other fallout from Washington and Tokyo with a missile test, it might make preparations for a launch - under full surveillance by U.S. military satellites - to rattle nerves in the region and force American concessions in its confrontation with Washington. A Defense Ministry official in Seoul, speaking on condition of anonymity, said the government was trying to verify reports about the Taepodong-2 missile. "So far there is not enough credibility" in the reports, he said, without giving further details. Earlier Friday, NHK television and the Kyodo News Agency in Japan, citing unnamed sources, said that movement had been observed near a missile base in northeastern North Korea since early this month. South Korean news media later cited unnamed government officials as saying that they, too, detected such activities but that there was no sign of an imminent test. Foreign Minister Taro Aso of Japan told a parliamentary committee in Tokyo that Japanese officials "understand that a missile has been brought to the site." Japan's chief cabinet secretary, Shinzo Abe, said: "At this point we do not feel there is imminent danger of a missile launch," adding that Japan had been gathering intelligence. American experts said that the Taepodong-2 ballistic missile has a range of more than 6,700 kilometers, or 4,200 miles, making it capable of hitting Alaska with a light payload. A different version of the Taepodong- 2, which U.S. experts have said was also under development, has a range of 15,000 kilometers, enough to reach the U.S. mainland. North Korea shocked Japan in 1998 by launching a Taepodong-1 missile over its territory and into the Pacific. That missile had a range of up to 4,000 kilometers, and may be capable of reaching some islands in the Hawaiian chain, as well as U.S. military bases in the region. The United States and North Korea have been locked in a standoff over the North's nuclear weapons programs. Washington has been increasing financial pressure on the isolated North to force it to return to nuclear disarmament talks, but the North has so far resisted such attempts, which it considers an effort to topple its Communist regime. On Thursday, The New York Times reported that top advisers to President George W. Bush were considering ways to improve relations with North Korea, including talks for a peace treaty with Pyongyang, once it returns to international talks on ending its nuclear weapons program. In a report in March, the California- based Center for Nonproliferation Studies, a nongovernmental organization, said North Korea did not have an operational missile that could hit the continental United States, and nor had it demonstrated the capability to make a nuclear weapon small enough to be part of a missile warhead. "North Korea would probably require several years and additional flight-tests to develop a reliable ballistic missile system capable of delivering a nuclear warhead to the continental United States," the report said.