An anonymous bomb threat e-mailed to Air China's Tokyo offices on Friday forced a passenger jet to make an emergency return to Japan, the Japanese Transport Ministry said. Four other flights were delayed.
The e-mail, written in Japanese and received in the early afternoon, urged the airline to suspend its flights or the writer would "bomb the aircraft," said Transport Ministry official Fumio Yasukawa.
"We suspect this is a threat related to the Olympics," he said, refusing to provide further details of the note or say whether any particular groups were suspected of sending it.
Police are investigating the case but they don't have a suspect yet, a Tokyo Metropolitan Police official said on condition of anonymity, citing department policy.
A flight carrying 70 people from Nagoya to Chongqing via Shanghai was forced to return to Japan after the threat was received, and it landed safely, he said. The flight departed from the central Japan airport for the second time later Friday after undergoing safety checks that found no problems, ministry officials said.
Another transport official, Morihiro Kawada, said Friday's bomb threat does not affect Japan's safety measures.
"We have already instructed all airlines flying between Japan and China to carry out maximum safety checks during the Olympics," he said. "We hope they all keep at it until the last day of the games."
Two other jets underwent safety checks and departed Fukuoka, in southern Japan, one headed to Beijing and one to Shanghai, Yasukawa said. Two more flights scheduled to leave Tokyo's Narita airport had also left after safety checks, he said.