TOKYO (Reuters) - Tokyo police plan to arrest four teenagers from U.S. military families living in Japan on suspicion of attempted murder, Kyodo news agency reported on Wednesday, as tensions simmered over U.S. bases in Japan.

The four, aged 15-18, are suspected of involvement in an incident in August in which a Japanese woman riding a motorcycle ran into a rope stretched across a road in Tokyo near Yokota Air Base and fractured her skull, Kyodo said, citing investigative sources.

Tokyo Metropolitan Police Department declined to comment on the case.

Mitsuru Takahashi, who is in charge of media relations at the public affairs office of Yokota Air Base, said the four have not been arrested and they have not been identified as suspects.

“The U.S. military has heard from the Metropolitan Police Department that such an incident had taken place... We hope that the victim will recover as soon as possible,” Takahashi said.

The alliance between the two countries has been jolted before by military accidents and crimes, including the 1995 rape of a 12-year-old girl by U.S. soldiers based in Okinawa that prompted huge anti-base protests.

Japanese police have also questioned a U.S. soldier about a fatal hit-and-run accident on the southern island of Okinawa.

Under an agreement between the two governments, U.S. forces based in Japan are not obliged to hand over personnel suspected of a crime outside the base unless they are charged, though they have sometimes done so in serious criminal cases.

There is disagreement as to whether the agreement applies to dependents, but previous cases that saw a delay in handing over U.S. military personnel suspected of serious crimes have caused outrage in Japan.

The Japanese government, led by Prime Minister Yukio Hatoyama who took power in September, and Washington are locked in a feud over the relocation of a U.S. Marine air base on Okinawa, which is home to about half of 47,000 U.S. troops stations in Japan.