Japan has not yet responded to Morgulov's remarks and has not responded to a CNN request for comment.

The US and Japanese navies last week wrapped up joint exercises in the East China Sea and Philippine Sea headlined by the USS Abraham Lincoln Carrier Strike Group.

Earlier in the month, the Abraham Lincoln led similar joint drills in the Sea of Japan, upon which Russia has a lengthy shoreline.

According to the US Navy, the US and Japan routinely hold joint naval exercises in the Indo-Pacific to "maintain stability in a free and open Indo-Pacific region."

A lingering World War II dispute

Japan on Friday described four disputed islands as "illegally occupied" by Russia, the first time in two decades it has used such language.

Per the report, Japan sees the islands as "Japanese territories over which Japan holds sovereign rights, but are currently illegally occupied by Russia."

While that dispute has simmered for decades, Japan's support for Ukraine has turned up the heat in the relationship between Moscow and Tokyo.

On Tuesday, Japanese Prime Minister Fumio Kishida agreed to provide food and medicine, additional financial support, small drones and protective face masks to Ukraine, according to a statement released by the country's Foreign Ministry.

Earlier this month, Japan expelled eight Russian diplomats and officials due to the war in Ukraine.

Japan's actions 'predictable and transparent'

Analysts said Moscow is jumpy right now and taking out frustrations on Japan.

"Japan and the US haven't done anything out of the ordinary ... nothing that would really seem to prompt this level of response," said James D.J. Brown, associate professor of political science at Temple University in Tokyo.

Drew Thompson, a senior research fellow at the Lee Kuan Yew School of Public Policy at the National University of Singapore, echoed those thoughts, saying increased military cooperation with the US is the sensible thing for Tokyo to do.

"Japan is slowly awakening to the security threats on its periphery, and it's doing so in a predictable and transparent way consistent with a democracy," Thompson said.

Cmdr. Hayley Sims, spokesperson for the US 7th Fleet based in Japan, described the joint exercises in the Sea of Japan in early April as "routine bilateral operations."

"Our training enhances the credibility of conventional deterrence by demonstrating the strength of our bilateral partnerships," Sims said.

But Russia has a different viewpoint.

"I think it really does show the increased jumpiness of the Russian side, their tendency now to view actions in their vicinity as always being potentially offensive," Brown said.

He said increased Japanese cooperation with NATO allies including Britain and France, countries with which Russia has disputes in Europe, exacerbate tensions in the Pacific.

"One thing that the Russians really dislike is that Japan in recent years has been strengthening cooperation with other countries beyond the United States," Brown said.

Russian provocations

Russia has been flexing its military muscles around Japan for the past few years, analysts said.

Satoru Mori, professor of contemporary international politics at Keio University in Japan, said there had been numerous Russian provocations in the past few months, like military drills on the disputed islands and tests of submarine-launched cruise missiles in the Sea of Japan.

"Russia has been stepping up military activities in the vicinity of Japan probably to demonstrate its ability to operate in the Far East even in the midst of invading Ukraine," Mori said.

"This is Japan responding to dynamics that began with the strengthening of Russia-China military cooperation," Thompson said.

"That's the change that's driving Japanese defense planning and political resourcing, rather than a direct response to these latest Russian threats," he said. "If anything it validates Japan's strategy to enhance its own ability to deter the use of military force against it."