Four American teenagers, all children of US military personnel, have been arrested on charges of attempted murder after a woman was knocked off her motorbike with rope strung across two poles, Japanese police said. The four suspects — two 15-year-old boys, a 17-year-old girl and an 18-year-old man — were taken into custody on Saturday, the Tokyo Metropolitan Police Department said. They are accused of causing a severe head injury to a 23-year-old restaurant employee by stringing a rope between poles across a road. US Forces in Japan was informed of the August incident in late October, a public information officer said. There was no clear explanation for the delay in the handover of the suspects to police, other than it involved rules between Washington and Tokyo covering US forces and their dependents in Japan. The US military presence and its impact on Japanese residents have been a thorny issue over the years.