REUTERS

Japan said a Chinese frigate sailed within 24 miles (38 km) of the contested territory, the islands known as the Senkaku in Japan and the Diaoyu in China, shortly after midnight, as reported by Reuters.

Japan's Vice Foreign Minister Akitaka Saiki summoned the Chinese ambassador in Tokyo to "express a serious concern," the government said in a statement.

"We are worried that this action raises tensions to a higher level," Japan's Chief Cabinet Secretary Yoshihide Suga said at a regular press briefing in Tokyo.

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"Related ministries are working together to deal with this and we will work closely with the U.S.," Suga said.

Read alsoChinese jets intercept U.S. spy plane over South China Sea – PentagonComplicating the situation for Tokyo, three Russian naval vessels also sailed close to the islands at around the same time as the Chinese warship, raising concern in Japan of a coordinated show of force by Beijing and Moscow.

Suga said the government was investigating to uncover any link between the movements of Chinese and Russian vessels.

China's Defense Ministry said on Thursday it was looking into the reports that one of its navy ships sailed close to the disputed islands, adding its navy had every right to operate in Chinese waters.

"Chinese naval ships sailing through waters our country has jurisdiction over is reasonable and legal. No other country has the right to make thoughtless remarks about this," it said in a statement sent to Reuters.

While the U.S. has not endorsed Tokyo's territorial claim to the islands, which lie about 220 km (135 miles) northeast of Taiwan, it has said the Japanese-controlled territory falls under its security treaty with Tokyo that obligates Washington to defend Japan against attack.

Read alsoChina to set up maritime "judicial center""We are aware of the reports and have been in touch with the Japanese government," U.S. Deputy Assistant Secretary of State for East Asian and Pacific Affairs, Colin Willett told reporters by telephone from Washington.

"Until I have a little more detail, I can't really comment on exactly what (Washington's) reaction is," she added.