The United States is warning that it would be a major international concern if North Korea launched a long-range ballistic missile. Reports by Japanese media say North Korea may be preparing to test-fire such a weapon.

A U.S. State Department spokesman said Friday that a missile launch would also violate an agreement reached in September at the last round of six-party talks on North Korea's nuclear program. 

On Friday Japanese broadcaster NHK quoted unidentified South Korean government officials as saying that satellite pictures show signs of activity at a launch site in northeastern North Korea. 

Japan's Defense Agency quickly responded, saying that Tokyo does not believe a launch is imminent.  However, Japanese Foreign Minister Taro Aso told a parliamentary committee that a launch would be no surprise.

In 1998, North Korea surprised Japan and governments around the world by firing a long-range missile over Japan into the Pacific Ocean.

Some information for this report was provided by AFP and Reuters.