A Chinese jet fighter flies above a CCTV camera and buildings on Pingtan Island, the closest point in China to the main island of Taiwan, in China's southeast Fujian province, on January 13, 2024. Greg Baker, AFP/file 

Japan is strongly alarmed by recent airspace breaches by China and Russia and other military activities by them around the country, Defense Minister Minoru Kihara said Tuesday.

Kihara's remarks came a day after a Russian military patrol plane flew over waters in the Sea of Japan north of Hokkaido three times, prompting an Air Self-Defense Force fighter jet to fire a signal flare for the first time ever, according to the Defense Ministry.

In late August, Japan also confirmed for the first time that a Chinese military spy plane violated Japanese airspace over waters in the East China Sea off islands in Nagasaki Prefecture in southwestern Japan.

"We have a strong sense of crisis over these kinds of cases that have occurred successively in such a short period in waters and airspace surrounding our nation," Kihara told a press conference in Tokyo, calling the airspace intrusion by Russia a "provocative act."

Kihara also noted that a total of eight Chinese and Russian naval vessels jointly sailed through the Soya Strait between Hokkaido and Sakhalin while passing from the Sea of Japan to the Sea of Okhotsk from Sunday to Monday.

Describing the signal flare use against the Russian plane as an "appropriate decision," Kihara said Japan will continue to monitor Chinese and Russian military activities "with strong interest" and make "necessary responses" to them.

In a separate news conference, Chief Cabinet Secretary Yoshimasa Hayashi said the Russian plane's airspace breach is "a severe infringement" of Japan's sovereignty and "totally unacceptable."

Japan, along with its close security ally the United States, has been more vigilant against China and Russia's strengthening military cooperation in recent years, especially since the full-scale Russian invasion of Ukraine began in February 2022.

Regarding a Japan Maritime Self-Defense Force destroyer's intrusion into Chinese territorial waters in July, Kihara said the captain of the ship was replaced that month following the incident but did not give a reason for the replacement.

Tokyo has told Beijing that the Suzutsuki entered the waters, despite repeated warnings by Chinese vessels, mistakenly and has also informed it of the captain's dismissal, according to diplomatic sources.