Japan's Defense Ministry released on Friday 13 minutes of video footage including radio communications with a South Korean warship which Tokyo claims locked its fire-control radar on a Japanese patrol plane in the Sea of Japan.
"Korean Naval Ship, Hull Number 971," a crew member of the Japanese Maritime Self-Defense Force P-1 patrol aircraft said over the radio to the South Korean ship.
"We observed that your FC antenna is directed to us. What is the purpose of your act?" the Japanese officer asked.
The Japanese aircraft asked the question three times to the South Korean ship but received no answer before the end of the video.
[Video clip released by Japan's Defense Ministry]
Some subtitles were added to the video clip for explanation and some of the crew's exchanges were cut for security reasons, but the images were not edited, the ministry said.
It is rare for the Japanese Defense Ministry to release video recordings of the SDF's patrolling and surveillance activities.
In the video, one crew member says he detected fire-control radar directed at the MSDF plane that the ministry says was about 5,000 meters away from the South Korean ship.
The plane's captain then orders him to check the status of the destroyer's weaponry, saying, "We are moving away for now." The crew said there was no indication that the ship's weapon was pointed in the plane's direction.
"The sounds are extremely strong," the crew member also says, referring to the intensity of the radio waves from the destroyer.
Fire-control radar is designed to accurately measure the direction and distance of a targeted object before launching an attack. The intensity of its radio waves tends to be constant and strong.
The South Korean Defense Ministry said in a statement it has "deep concern and regret" over Japan's release of the video clip just one day after the two countries held a video conference to avoid any misunderstanding.
The ministry is disappointed that the Japanese aircraft flew low around the South Korean ship to threaten it while the vessel was just carrying out a humanitarian operation to look for a North Korean fishing boat in distress, it said.
It continued to assert that the South Korean destroyer did not use fire-control radar on the Japanese patrol plane.