Prime Minister Shinzo Abe made the pledge when meeting with visiting US Defense Secretary Ashton Carter late Wednesday, the German news agency dpa reported from Tokyo.
The Japanese premier also asked for further US cooperation to reduce the impact of its military presence in the area.
Nearly one-fifth of Okinawa's main island is occupied by US military facilities.
Many locals oppose the proposed US base, intended as a replacement for one in a densely-populated area of the island.
Ashton Carter also met with his Japanese counterpart Gen Nakatani Wednesday, and the two agreed to speed up work on revising defense cooperation guidelines to be released in late April.
The Shinzo Abe cabinet last year approved a greater use of force by its military overseas with an eye to increasing the role of the Japanese military and cooperation with the US amid China's increasing maritime presence in the East China Sea.
