Roger Federer of Switzerland returns the ball during the match against Novak Djokovic of Serbia at the ATP World Tour Finals at the O2 Arena in London  Falcons Deion Jones Jersey , Nov. 17, 2015. Federer won 2-0. (XinhuaHan Yan) Defending Champion Novak Djokovic of Serbia returns the ball during the match against Roger Federer of Switzerland at the ATP World Tour Finals at the O2 Arena in London, Nov. 17, 2015. Novak Djokovic lost 0-2. (XinhuaHan Yan) Roger Federer of Switzerland returns the ball during the match against Novak Djokovic of Serbia at the ATP World Tour Finals at the O2 Arena in London  Falcons Keanu Neal Jersey , Nov. 17, 2015. Federer won 2-0. (XinhuaHan Yan) Roger Federer of Switzerland returns the ball during the match against Novak Djokovic of Serbia at the ATP World Tour Finals at the O2 Arena in London, Nov. 17, 2015. Federer won 2-0. (XinhuaHan Yan) Defending Champion Novak Djokovic of Serbia returns the ball during the match against Roger Federer of Switzerland at the ATP World Tour Finals at the O2 Arena in London  Falcons Sean Harlow Jersey , Nov. 17, 2015. Novak Djokovic lost 0-2. (XinhuaHan Yan) Defending Champion Novak Djokovic of Serbia reacts during the match against Roger Federer of Switzerland at the ATP World Tour Finals at the O2 Arena in London, Nov. 17, 2015. Novak Djokovic lost 0-2. (XinhuaHan Yan) Roger Federer (L) of Switzerland and Novak Djokovic of Serbia are seen during the match against Novak Djokovic of Serbia at the ATP World Tour Finals at the O2 Arena in London  Falcons Duke Riley Jersey , Nov. 17, 2015. Federer won 2-0. (XinhuaHan Yan) Roger Federer of Switzerland returns the ball during the match against Novak Djokovic of Serbia at the ATP World Tour Finals at the O2 Arena in London, Nov. 17, 2015. Federer won 2-0. (XinhuaHan Yan) Coral reefs are seen along the coast near the U.S. Marine base Camp Schwab  Falcons Takkarist McKinley Jersey , off the tiny hamlet of Henoko in Nago, on the southern Japanese island of Okinawa, in this file aerial photo taken by Kyodo October 29, 2015 file photo. Mandatory credit REUTERSKyodo

TOKYO - An American man working at a U.S. military base in Japan was arrested on Thursday on suspicion of dumping the body of a 20-year-old Japanese woman  Falcons Isaiah Oliver Jersey , police said, a case likely to stir anti-U.S. sentiment ahead of a visit by President Barack Obama.

The 32-year-old civilian working at the base on the island of Okinawa admitted to abandoning the corpse but did not make any comments about whether he had killed the woman, an Okinawa police spokesman said.

Japanese Foreign Minister Fumio Kishida summoned Caroline Kennedy, U.S. ambassador to Japan  Falcons Calvin Ridley Jersey , to lodge a protest.

"I expressed a strong regret to Ambassador Kennedy and lodged a stern protest. I told her an incident like this is inexcusable and that I feel strong indignation," Kishida told reporters.

Kennedy told Kishida the United States would redouble its efforts to prevent similar incidents, the foreign minister said.

In Washington, the Pentagon said the individual was a contractor  Falcons Alex Mack Jersey , but did not name him.

Spokesman Peter Cook said the Pentagon would provide "complete cooperation" in the investigation, while State Department spokesman John Kirby expressed condolences.

"This is a terrible tragedy and it's obviously an outrage," Kirby told a daily news briefing. "We're treating this situation with the utmost seriousness."

Obama, who is to attend a Group of Seven summit in Japan next week  Falcons Vic Beasley Jr Jersey , will become the first U.S. president to visit Hiroshima, a city destroyed by a U.S. atomic bomb 71 years ago.

Okinawa, the site of a bloody World War Two land battle, hosts the bulk of U.S. military forces based in Japan since the war  Falcons Matt Ryan Jersey , and many residents resent what they see as an unfair burden.

U.S. installations take up about 18 percent of Okinawa's land area and past incidents involving Americans have fueled resentment.