North Korea Monday threatened to retaliate if anyone tries to shoot down a satellite it plans to launch, saying interfering with the country's peaceful space activity would mean war.

The statement comes as South Korea and the United States began their annual war drill Monday, in what could be an indication that North Korea may try to launch the supposed satellite during the joint exercise that will continue through March 20, Yonhap News Agency reported.

"We will retaliate any act of intercepting our satellite for peaceful purposes with prompt counter strikes by the most powerful military means," a spokesman for the General Staff of the Korean People's Army was quoted as saying, specifically naming South Korea, the U.S. and Japan.

"Shooting our satellite for peaceful purposes will precisely mean a war," the spokesman said in a statement carried in English by the Korean Central News Agency (KCNA).

U.S. and South Korean intelligence sources believe the launch may be a cover for test-firing a long-range missile that is theoretically capable of striking Alaska or Hawaii. U.S. and Japanese military officials have suggested they are considering intercepting if North Korea does launch a missile.

The North also said it will cut off military communications with South Korea, the last official inter-Korean channel that remains open, during the 12-day joint drill. Pyongyang ordered its entire military to be fully combat ready, saying the joint war exercise is aimed at launching a "second Korean War."

"As an immediate measure we will enforce a more strict military control and cut off the North-South military communications," the military spokesman said.

A spokesman for the South Korean government said the suspension of military communications will immediately lead to a closure of the border. South Koreans planning business trips to a joint-industrial complex in the North Korean border town of Gaeseong will have to cancel their plans, said Unification Ministry spokesman Kim Ho-nyoun. South Koreans cannot cross the border without approval by North Korea given through the last-remaining inter-Korean channel.

"Our government will announce our position later in the morning," Kim said.