File photo taken on a marine surveillance plane B-3837 shows the Diaoyu Islands and nearby islands.Photo:Xinhua

 Japan's Ministry of Defense hyped on Monday that Chinese and Russian warships were spotted near the Diaoyu Islands in the East China Sea almost at the same time earlier in the day. Chinese and Russian vessels have the right, albeit different, to freely navigate in the contiguous zone of the Diaoyu Islands of China, experts pointed out, saying that the Russian Navy's recent military activities in the West Pacific is a warning to Japan amid Japanese sanctions on Russia over the Ukraine crisis.

A Russian frigate entered the Diaoyu Islands' contiguous zone from 7:05 am to 8:16 am on Monday, and a Chinese frigate sailed in the same area for about six minutes from 7:44 am, Kyodo News reported on Monday, citing the Japanese Defense Ministry.

The Chinese frigate involved is a Type 053H3 frigate, equipped with YJ-83 anti-ship missiles, HHQ-7 air defense missiles and 37-millimeter-caliber guns, according to a press release by the Japanese Defense Ministry. 

Japan has "lodged a protest" with China after the incident, which was the first time since June 2016 when Chinese and Russian naval vessels had been spotted entering the contiguous zone at around the same time, Kyodo News said.

Zhao Lijian, a spokesperson of China's Ministry of Foreign Affairs, said at Monday's regular press conference that the Diaoyu Islands and its affiliated islands are China's inherent territories. Chinese vessels' maritime activities in waters off the islands are fully legitimate, and Japan has no right to make irresponsible accusations, he said.

Tian Shichen, founder of the Global Governance Institution and director of the International Center for the Law of Military Operations, told the Global Times on Monday that a contiguous zone overlaps with an exclusive economic zone, which means foreign warships have the right to navigate freely in any country's contiguous zones as long as they abide by the domestic laws set by the coastal country in accordance with international law.

Chinese and Russian warships can freely navigate in the Diaoyu Islands' contiguous zone, but on different legal bases, Tian said.

The Chinese vessel navigated in the Chinese contiguous zone over which China has sovereign rights and jurisdiction, while the Russian vessel navigated in the area freely because of the right of free navigation in any contiguous zone in accordance with international law, Tian explained.

It is an act of safeguarding national sovereignty that Chinese warships patrol and monitor the Diaoyu Islands, Zhou Yongsheng, a professor at the Institute of International Relations at China Foreign Affairs University, told the Global Times on Monday.

According to press releases by Japan's Ministry of Defense Joint Staff, a number of Russian warships circumnavigated Japan in June.

Zhou said that Russia, which is having a military operation against Ukraine, has island disputes with Japan, and Russian naval activities in the West Pacific aim at deterring Japan from taking reckless moves.

Russia's recent moves serve as a warning to Japan amid Japanese sanctions on Russia, and aim to ease Western pressure on Russia because of the Ukraine crisis, analysts said.