North Korea accused the U.S. military of making provocative moves along the tense border on the divided Korean peninsula, warning Saturday of "unpredictable military conflicts."

The rare threat came as North Korea was apparently gearing up to test-fire a long-range missile believed capable of reaching U.S. territory. Pyongyang has also stepped up its war of rhetoric against the South over Seoul's tough stance toward its communist neighbor.

North Korea's military said U.S. troops advanced as close as 100 feet from the Military Demarcation Line in the western border and took pictures of a North Korean military post last month. It also said more than 60 U.S. patrols approached to within 330 feet of the boundary this year.

The U.S. provocations "at a time when the North-South relations are inching close to the brink of a war may touch off unpredictable military conflicts," the North's military said in a message sent to the South, according to the North's official Korean Central News Agency.

"If the U.S. forces keep behaving arrogantly ... the (North's military) will take a resolute counteraction." It did not elaborate.

South Korea's Defense Ministry dismissed the North's accusation as groundless, calling the U.S. military moves "legitimate activities" because the U.S.-led U.N. Command oversees the Demilitarized Zone that separates the two Koreas.

The U.S. stations 28,500 troops in South Korea to help deter the North's possible aggression.

A spokesman of the U.S. military was not immediately available for comment.

The U.N. Command oversees the cease-fire that ended the 1950-1953 Korean War. North Korea has long maintained that the U.N. Command is irrelevant and a thinly veiled U.S. effort to claim international legitimacy for its forces here.

Although other nations contributed forces during the Korean War, U.S. troops are the only fighting elements facing North Korea left on the peninsula in addition to the South Korean military.