A Russian Yasen-class nuclear-powered submarine sails through the Soya Strait north of Hokkaido on Nov. 11, 2024. (Japan's Ministry of Defense)

Russia’s most advanced submarine was spotted for the first time in waters near Japan, the country’s military announced Monday.

A Yasen-class nuclear-powered submarine accompanied by a flotilla of Russian vessels passed through the Soya Strait, a 27-mile-wide international waterway that separates Japan’s northern island of Hokkaido and Russia’s Sakhalin Island, according to a Joint Staff news release. The transit happened around 8 a.m. Monday.

The submarine and three other vessels — an Udaloy-class frigate, a Marshal Nedelin-class tracking ship and a Baklazhan-class rescue tug — were seen about 50 miles northeast of Cape Soya heading west, the release said.

The Japan Maritime Self-Defense Force dispatched a P-3C aircraft from Fleet Air Wing 2 to surveil the group, according to the release.

“It was the very first time that the Maritime Self-Defense Force confirmed a Yasen-class nuclear-powered submarine,” the release said.

Russian military ships and planes have ramped up their activity near Japan in recent months.

A Russian IL-38 reconnaissance plane entered Japanese airspace three times on Sept. 23, prompting Tokyo to scramble fighter jets to intercept and ultimately warn off the aircraft with flares.

On Sept. 12, a pair of Russian Tu-142 patrol planes circled Japan’s four main islands for the first time in five years. They flew a route that spanned from Okinawa in the south to Hokkaido in the north, the Joint Staff said at the time.

On Sept. 1, two Russian navy corvettes were spotted 19 miles north of Cape Soya heading west, according to USNI News on Sept. 6.