TOKYO -- A South Korean destroyer that locked a fire-control radar on a Japanese patrol plane earlier this week did so for several minutes, Japanese government sources said, suggesting that the incident may not have been an accident as Seoul had claimed.

The radar was trained on the aircraft for several minutes, not seconds, and more than once, the sources said. The Defense Ministry issued a statement Saturday criticizing South Korea for the "extremely dangerous" act.

Japan announced Friday that the South Korean vessel trained its radar on a P-1 patrol plane belonging to Japan's Maritime Self-Defense Force. "This is the kind of thing that happens right before an attack," Defense Minister Takeshi Iwaya said.

South Korean media reported that the destroyer at the time had been using all of its radars, including its fire-control radar, in order to search for a drifting North Korean vessel, citing defense officials. The South's Defense Ministry said only that the warship was engaged in routine operations, and was not purposefully tracking the Japanese plane.

But Japan has expressed skepticism. "Fire-control radars are used to determine the exact direction and distance of a target before an attack, and are not suited for wide-range searches," the Saturday statement said.

Meanwhile, South Korea's Ministry of Unification announced Saturday that it had rescued three people and recovered one body from a North Korean vessel in international waters in the Sea of Japan on the day the radar incident occurred. They were purportedly handed over to the North Saturday.

The Japanese side confirmed a South Korean rescue ship was sailing near the destroyer. The Unification Ministry's announcement may have been an attempt to strengthen South Korea's position.

Still, an MDSF source said that "it is hard to imagine why someone would train a fire-control missile on a friendly vessel." The recent incident is unusual given that Japan and South Korea cooperate on defense issues.