The military is considering sending a helicopter to respond to any further Japanese spy planes buzzing Korean warships. The chopper would block the flight path of any Japanese patrol plane if it came close to a Korean destroyer, as happened on several occasions in the past few weeks.

The idea was mooted by the Joint Chiefs of Staff during a briefing of the ruling Minjoo Party on Thursday. After a meeting of the National Security Council at Cheong Wa Dae the same day, an official said, "We're very concerned about the repeated threateningly close flybys of Japanese patrol aircraft and decided to respond firmly to prevent a recurrence."

Navy destroyers and new patrol corvettes are capable of carrying choppers. "No chopper is a direct match for a patrol plane," a military spokesman said. "But no fast-flying plane would come close to a warship if a chopper was hovering nearby” since the plane cannot swerve fast enough.

The military is also considering sending stronger warning signals to Japanese aircraft. "Warning signals are sent in stages as [Japanese patrol aircraft] come closer and closer ," said Cho Jeong-sik, a Minjoo Party lawmaker who attended the JCS' briefing. "The JCS wants to send signals earlier than it does now."

That means warships could start sending warning signals when a foreign patrol aircraft comes within 10 miles of them instead of just five as at present.

The JCS could also scramble nearby patrol aircraft if Japanese coat-trailing continues. A JCS officer said, "We are working to come up with more elaborate responses when allies' planes perform a threatening maneuver over our warships."