South Korean media have reported that North Korea's preparations to launch a military spy satellite are in the final stage.

Pyongyang earlier said that last November's launch of its first military satellite, Malligyong-1, was successful. It announced plans to launch three more military reconnaissance satellites this year based on its five-year defense program.

South Korea's Yonhap News Agency on Sunday quoted a government source as saying preparations are essentially completed. The assessment was based on the situation at a facility in Tongchang-ri, where North Korea's Sohae satellite-launching station is located in the country's northwest.

Citing the source, Yonhap also reported that it is highly likely that the launch will be timed around major North Korean political events this month. On Monday, the North will mark the birthday of Kim Il Sung, the country's founder and the grandfather of its current leader Kim Jong Un.

South Korea's Defense Minister Shin Won-sik has said Pyongyang may go ahead with the launch as early as mid-April.

South Korean military and US forces have been on high alert, continuing their monitoring and surveillance activities.