Japan has lodged a diplomatic protest against China on Friday after a Chinese warship entered Japanese waters and sailed near the Japanese-controlled Senkaku Islands in the East China Sea.

Japan's Foreign Ministry said Beijing's incursions into Tokyo's territorial waters heightened tensions in the region and raised serious concerns among Japanese troops stationed in the islands.

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The ministry said a Chinese vessel entered Japan's territorial waters surrounding the Senkaku Islands at around 5:00 am (15:30 GMT) on Wednesday, prompting the officials to lodge the complaint.

In a statement, Japan's Vice Foreign Minister Akitaka Saiki. said he had summoned Chinese Ambassador Cheng Yonghua and lodged the protest at 2:00 am on Friday.

In the protest, Saiki pointed out that the Chinese Navy vessel's entry into the border zone is an "action that unilaterally heightens tensions."

Russian ships

To make matters worse, Japanese coast guards also spotted three Russian ships sailing near the islands at about the same time that the Chinese warship entered the waters, demonstrating an apparently coordinated show of force by Beijing and Moscow, he pointed out.

Saiki said Chinese coast guards usually sail in the waters surrounding the Senkaku Islands, but the incident was the first time a Chinese ship entered the waters of Japan.

He said Tokyo will seek the advice of Washington and will confer with the global community on the best thing to do to handle China's assertiveness in the region.

"Japan will cooperate closely with the USA and the global community and strongly urge China not to engage in any action that would unilaterally heighten tensions," he said.

International waters

Meanwhile, China's Foreign Ministry has denied Japan's claims, saying that the Chinese Navy vessel was on routine patrol in international waters.

China's Foreign Ministry spokesperson Hua Chunying said that the Chinese ships did not violate Japanese territorial waters as it is being claimed by Japan according to the United Nations Convention on the Law of the Sea (UNCLOS).

"I would advise that Japanese media and the government better study international laws before making any report or comment," she said.

Japan has expressed concern that China will try to expand its reach in the East China Sea.

U.S. President Barack Obama has noted that according to a mutual security pact, Washington is obligated to come to the aid of Tokyo if Japanese-controlled territories in the East China Sea come under attack. 

TagsSenkaku Islands, Japan, East China Sea, Japanese coast gurads, china warship, china