NEW : Japanese defense minister says they are lodging protests with Japanese authorities . The two year - olds are accused of killing a Japanese woman on Okinawa . Questions over the U.S. military presence on Okinawa have boiled over in the past . The U.S. government is ` ` extremely concerned '' by the allegations , he says .
NEW : Japanese defense minister says officials are lodging protests with U.S. authorities . The two 23-year-olds are accused of raping a Japanese woman on Okinawa . Tensions over the U.S. military presence on Okinawa have boiled over in the past . The U.S. government is `` extremely concerned '' by the allegations , ambassador says .