Japan's Kyodo news agency says U.S. reconnaissance satellites show recent activity by North Korean military vehicles loaded with Rodong missiles, sparking fresh concerns that the communist state may be preparing to conduct a missile test.

Citing sources close to Tokyo and Washington, Kyodo news agency said U.S. satellite pictures showed movements of vehicles, soldiers and communication equipments in the Wunjeon district in North Korea's Northern Pyongan province.

The sources also reported on signs of combustion experiments of missile engines in North Hamgyung province. They said this particular site was rebuilt last July after it was demolished during Pyongyang's failed test-firing of Rodong-2 missiles in 2002, adding that two cases of combustion experiments have been detected since the year's beginning.

The Washington Post quoted a U.S. military official as saying the missile Pyongyang may test-fire this time appears to be a new projectile with a range of more than 3,500 kilometers.

Meanwhile, Japan's Yomiuri newspaper cited some Japanese officials as suggesting the matter is likely another of Pyongyang's brinkmanship tactics designed to unnerve its neighboring countries.