Japan said Friday that it would strengthen intelligence-gathering and monitoring after the Russian Defense Ministry announced a day earlier that two navy submarines had test-fired Kalibr cruise missiles in the Sea of Japan, the latest in a series of high-profile military exercises in the region since Moscow’s invasion of Ukraine.

“In recent years, Russian military activities, including the deployment of state-of-the-art equipment and training exercises, have tended to increase in the vicinity of Japan,” Defense Minister Nobuo Kishi told a news conference. “We will continue to collect information and conduct vigilant monitoring with a sense of concern.”

On Thursday, the Russian Defense Ministry announced that submarines belonging to the country’s Pacific Fleet had launched the advanced cruise missiles, the same weapons being used in Ukraine, from submerged positions in the Sea of Japan, successfully hitting a mock target designed to resemble an enemy vessel. The ministry did not reveal the date or actual location of the launches.

It said more than 15 warships and supporting vessels, as well as naval aircraft, had taken part in the exercise.

Russian military activity in the area has ticked up in recent weeks, including on nearby disputed islands known in Japan as the Northern Territories. On March 28, Tokyo lodged a protest with Moscow through diplomatic channels over drills on the islands involving around 3,000 troops.

According to the Japanese Defense Ministry, the Russian military has used exercises in the Sea of Japan, Sea of Okhotsk and on or near the disputed islets to highlight its advanced weaponry and ability to operate in both the European and Asian theaters simultaneously amid the war in Ukraine.

"Russia is increasing the number of sea-launched cruise missile Kalibr-equipped vessels as part of efforts to modernize its conventional forces, and the two submarines believed to have launched the missiles are suspected to have been deployed to the Far East since last November,” Kishi said, adding that the latest exercise was conducted after their deployment.

“It’s believed that the Russian Navy intends to demonstrate the modernization of its naval power both domestically and internationally, even under the current circumstances,” he added, referring to the war in Ukraine.

Ties between the two countries have sunk to fresh lows after the invasion.

Thursday’s Russian missile test also came a day after the U.S. 7th Fleet said it was conducting joint naval exercises with the Maritime Self-Defense Force in the same waterway. Those drills, which have involved the USS Abraham Lincoln aircraft carrier and MSDF warships, were largely seen as a show of force amid North Korea’s recent missile launches and work to repair its main nuclear test site.

The Lincoln’s deployment was the first to waters off the Korean Peninsula since November 2017, when three U.S. aircraft carriers operated in the region in response to soaring tensions over Pyongyang’s nuclear program.

North Korea celebrated the 10-year anniversaries of leader Kim Jong Un’s ascension to top leadership posts on Monday and Wednesday and marked its most important holiday on Friday, the anniversary of the birth of Kim’s grandfather and founder of the country, Kim Il Sung, 110 years ago, with an apparent military parade.