The Prime Minister's Official Residence, the Imperial Palace and other key facilities have been allocated top-priority status for protection under a prospective missile defense program, according to an operational plan made available Wednesday.

The plan envisages joint operations between the Self-Defense Forces and U.S. military forces in Japan for intercepting missiles in the event of an attack on Japan.

The Defense Agency would also consider undertaking joint combat action with the United States to counter an attack even when the target is ambiguous, while taking relevant legal issues into account, according to the plan.