TOKYO - Japan's prime minister expressed his "strong indignation" Friday after an American working on a U.S. military base in Okinawa was arrested on suspicion of abandoning the body of a woman who disappeared last month.

"I have no words to express, considering how the family feels," Prime Minister Shinzo Abe told reporters. "We urge the U.S. side to take thorough measures to prevent the recurrence of such events."

The arrest sparked outrage on Okinawa, where anti-U.S. military sentiment is high because of a heavy American troop presence, and repeated instances of violent encounters between American military personnel and locals. It could fuel further opposition to the relocation of a U.S. Marine Corps air station on the southern Japanese island, a long-delayed project that Abe has been trying to push forward in the face of large protests.

Get Breaking News Delivered to Your Inbox

The infamous 1995 rape of a schoolgirl by three U.S. servicemen sparked the initial outcry that lead to an agreement to relocate the Marine Corps Air Station Futenma to a less crowded part of the island.

Police said Kenneth Shinzato, 32, was arrested Thursday after he was questioned and investigators found the body at a location he provided, a forest in central Okinawa.

Investigators determined that the body is that of a 20-year-old woman missing since April 28, when she messaged her boyfriend that she was going for a walk.

Police said they suspect Shinzato was also responsible for her death. He has not been charged.

In Washington, Defense Department spokesman Peter Cook said the man arrested was a U.S. military contractor. "This is an appalling tragedy," he said. The U.S. military extends its "deepest sympathies to the people of Japan, and express our gratitude for the trust that they place in our bilateral alliance and the American people."

Kyodo News agency said Shinzato used to be a Marine.

State Department spokesman John Kirby said the U.S. military was cooperating fully with local authorities in their investigation. "This is a terrible tragedy and it's obviously an outrage," he told reporters in Washington.

Okinawa Gov. Takeshi Onaga said he was "outraged" and that the death of the woman broke his heart. "As I look back at all the developments to date, I'm simply speechless," he said.

Onaga has spearheaded opposition to the relocation of U.S. Marine Corps Air Station Futenma from a densely populated neighborhood in central Okinawa to another site on the island, saying the facility should be moved away from Okinawa instead.

Foreign Minister Fumio Kishida summoned U.S. Ambassador Caroline Kennedy to convey his "regret" over the crime.

Kennedy said: "Nothing that I can do or say will make up the loss or to bring her back, but I want to express to you my determination and that of my military colleagues to cooperate fully with Okinawan police and the Japanese government, and we will double our efforts to make sure this will never happen again."

Okinawa is home to more than half of about 50,000 American troops based in Japan. Many Okinawans complain about crime and noise connected to the bases.