WASHINGTON - American defense officials say they expect another North Korean missile launch in the next several days.

The officials say the U.S. has increased its surveillance. The increased scrutiny follows the sighting of a North Korean missile launcher that is being moved around. The construction of VIP seating in the eastern coastal city Wonsan has also been spotted. The experts cite new surveillance from satellites, drones and other aircraft. It's unclear what type of missile may be tested.

North Korea, which is banned by the U.N. from conducting long-range missile tests, says it is in the final stages of developing an intercontinental ballistic missile, fitted with a nuclear warhead, that could reach the U.S. mainland. Experts say the North may be able to reach such capability in the next couple of years.

Earlier this month, Pyongyang fired off four ballistic missiles into the Sea of Japan, reportedly reaching within 120 miles of Japan's shoreline.