Japan and China are trading a new round of criticism after Japanese military aircraft spotted seven Chinese warships in waters off a southern island not far from a chain of isles at the center of a heated territory dispute. China said the ships were on a routine training mission.

The Chinese ships were sighted Tuesday about 49 kilometers (30 miles) from the island of Yonaguni, in Japan's Okinawa prefecture (state), according to Japan's Defense Ministry. They were about 200 kilometers (125 miles) from a chain of small islands that have sparked a heated dispute between Japan and China.

The ships were believed to be returning to China after training in the Pacific. Japan's Defense Ministry on Wednesday said the ships were not headed for the disputed islands, but said it was the first time the Chinese navy has been spotted using the narrow sea passage near Yonaguni.

Defense Minister Satoshi Morimoto said Japan is monitoring the ships' movement. Japan considers the area part of its contiguous waters, but it is not illegal for foreign vessels to transit them.

It is not unusual for the Chinese navy to transit waters around Okinawa en route to the Pacific, but they usually go through wider straits. The ships included frigates, a guided missile destroyer, a supply ship and two submarine rescue vessels. Defense Ministry officials said the ships might have been trying to avoid an approaching typhoon.

China's Defense Ministry said the ships were on a scheduled cruising exercise and were acting in a manner that was "appropriate and legal."

Underscoring China's sharper stance, it also protested the scrambling of a Japanese military plane in the direction of the disputed islands, calling that a "gross violation" of Chinese sovereign rights.