Beijing Reuters, Kyodo

China's Defense Ministry said Friday that Japanese surveillance activities threaten the safety of Chinese ships and aircraft.

The complaint came two days after Japan said it had been scrambling defense jets at a rate unseen since the Cold War. The Air Self-Defense Force said the scrambles were in response to Russian bombers probing its northern skies and Chinese combat aircraft intruding into its southern airspace.

China's Defense Ministry, in a statement faxed to journalists, said Chinese Air Force activities accord with both international law and norms.

"In recent years, Japanese ships and aircraft have often followed and monitored for lengthy periods and at close distances Chinese ships and aircraft, threatening the safety of the Chinese side," it said. "This is the cause of the safety issue in the seas and air between China and Japan," the ministry said.

"China has a grip on the tracking and surveillance by Japanese ships and aircraft, and takes necessary steps to deal with it," the ministry said, without elaborating.

Japan says the Chinese fighter incursions are concentrated in the East China Sea, close to the Senkaku Islands.

Coast guard ships and fighter aircraft from both sides routinely face off around the islands, fueling fears that an accident could spark a clash.

In Tokyo on Friday, the Japan Coast Guard said three Chinese coast guard ships had intruded into Japanese territorial waters around the disputed Senkakus on Friday morning.

The intrusion, which followed one on April 4, was the 11th of its kind this year.