Shozaburo Jimi, a former Japanese minister for financial services and postal reform who served in the government of Prime Minister Naoto Kan, said there is an independence movement on Okinawa that could take violent action.
"Okinawa has long had a history of independence movements and movements for self-governance. I hope those things will not blaze up," he said at a news conference. "There's a possibility that (Okinawa) will say it will become an independent state. Domestic guerrilla (attacks) could occur as a result of separatist movements.''
Jimi said "terrorist bombings" could hit Tokyo.
Japan annexed the Ryukyu archipelago, which includes Okinawa, in 1872. During World War II, U.S. forces invaded Okinawa. The battle, the last major U.S. Pacific campaign, lasted from April 1 until June 21, 1945.
The battle resulted in more than 62,000 U.S. military casualties, of whom more than 12,500 were killed or missing. Japanese military losses were estimated 95,000 combatants killed and 7,400 captured.
Civilians also suffered greatly during the assault, with an estimated quarter of the population killed.
The U.S. government returned the islands to Japanese administration in 1972. Under the 1960 Treaty of Mutual Cooperation and Security, the U.S. Forces Japan has maintained a presence of 27,000 personnel, including 15,000 U.S. Marines, and it is this ongoing U.S. military presence that concerns Jimi.
Okinawans have grown weary of the presence of U.S. military forces, saying Tokyo unduly burdens Okinawa by forcing it to host more than half of the 47,000 U.S. military personnel deployed in Japan.
Okinawans for years protested the heavy U.S. military presence due to accidents and crimes committed by U.S. soldiers, who aren't subject to local or Japanese law under the terms of the Status of Forces Agreement between Japan and the United States.
Underlining Okinawan frustration, last Sunday about 4,000 people marched in Tokyo's upscale Ginza district to protest the presence of U.S. military forces. Takeshi Onaga, mayor of the prefectural capital Naha, told protesters, "Our anger has been boiled to its peak."
Jimi noted that such frustration if not resolved could encourage Okinawans to press for secession from Japan, but, more worryingly, lead to domestic terrorism.
Jimi's remarks, in advance of a planned weekend visit by Japanese Prime Minister Shinzo Abe to Okinawa, were interpreted by analysts as an effort to pressure the ruling administration to address Okinawan concerns about the U.S. military presence.
How much leverage the protest may have is unclear. Despite rising protests by Okinawan politicians, Tokyo has remained adamant on its plan to relocate the U.S. Marine Futenma Air Station from a residential district of Okinawa to a sparsely populated shoreline area rather than downsize the U.S. military's island presence.