An Air Nippon jetliner and an unidentified fighter jet passed within close proximity of each other Friday over the sea around 65 km northwest of Naha, Okinawa Prefecture, the Transport Ministry said Tuesday. At the point where the two craft were closest, there was only a 60-meter altitude difference between them, ministry officials said. The pilot of the 103-passenger airplane, which left Fukuoka for Ishigaki Island in Okinawa Prefecture, was flying at an altitude of 8,500 meters at 1:50 p.m. when he received information from Naha air-traffic controllers that an aircraft operating under visual flight rules was approaching, ministry officials said. Noticing the jet ascending from about 150 meters below, the pilot of the Boeing 737-500 took evasive action in accordance with its traffic alert and collision avoidance system, they said. The pilot reported to the Transport Ministry on Monday that the two planes crossed over twice with a minimum altitude separation of about 60 meters and that the unidentified jet might have been an F-15 or F-16 fighter. No one on the Air Nippon jet was injured in the incident, according to the ministry. Ministry officials said they suspect the unidentified jet fighter was either operated by the United States military stationed in Japan or the Self-Defense Forces and were calling on both parties to confirm the situation. Both the U.S. military and the ASDF have training zones to the north of the airspace where the incident took place. Later in the day, however, officials at the Defense Agency's Air Staff Office said there were no Air Self-Defense Force aircraft in the area in question.