Several Japanese citizens protest took place in the vicinity of the U.S. Embassy in Tokyo over the alleged two sexual assault cases (recorded Okinawa Island) involving U.S. servicemen.

The first case involves a member of the Air Force (named Brennon R. E. Washington, 25). A spokesman for the Naha District Court told CNN that he is accused of sexually assaulting ("non-consensual sexual intercourse" and "indecent kidnapping") a 16-year-old girl.

The other case involves a Marine whose name has not been disclosed. He was accused of assaulting a 21-year-old woman.

Around 50,000 U.S. troops are in Japan.

Due to a bilateral security pact, about 50,000 U.S. troops are deployed in Japan. It is estimated that half of them are in Okinawa (a strategic location for dealing with growing tensions with China).

Japanese Chief Cabinet Secretary Yoshimasa Hayashi told reporters that his country "takes seriously" such events which are "extremely regrettable" and even more so when they allegedly occurred within a matter of months.

According to the secretary, Vice Foreign Minister Masataka Okano expressed his regret to the United States and Ambassador to Japan Rahm Emanuel requested disciplinary and preventive measures.

Hayashi said, "I believe that the U.S. side also takes this matter seriously (...) Criminal cases and accidents by U.S. military personnel cause great anxiety to local residents, and they should never occur in the first place."

"I believe that the U.S. side also takes this matter seriously (...) Criminal cases and accidents by U.S. military personnel cause great anxiety to local residents, and they should never occur in the first place."

On the other hand, Brig. Gen. Nicholas Evans, commander of the 18th Wing at Kadena Air Base in Okinawa, said he was "deeply concerned by the severity of this allegation and I regret any anxiety this has caused."

U.S. officials pledged that their military would cooperate fully with the investigation by local authorities and the courts.