A Japanese daily says the United States and Japan have begun drafting a joint operations plan for responding to possible contingencies on the Korean Peninsula.

The Asahi Shimbun said Thursday that "Operation Plan (OPLAN) 5055" focuses on Japan opening its ports, military bases and other facilities to assist American troops in the event of a war on the peninsula.

The plan also includes specific roles that the U.S. and Japanese troops will play in the event of a North Korean missile attack.

The two sides are also discussing details on a missile defense system and joint exercises to prepare for attacking North Korean bases.

OPLAN 5055 will be an upgraded version of an operation plan in concept format(CONPLAN) drafted by the two nations in 2002.

CONPLAN is an operation plan in an abbreviated format that would require considerable expansion or alteration to convert it into an OPLAN.

OPLAN refers to an operation plan in complete format for the conduct of joint operations that can be used as a basis for development of operation orders.(OPORD)