Three Russian Navy vessels traveled through the 65-kilometer waterway separating Okinawa’s Yonaguni and Iriomote Islands late last week, according to the Japanese Defense Ministry.

The announcement Saturday was the first time the ministry had revealed that Russian warships had passed through the waterway, which sits about 150 km from Taiwan, local media reported. The flotilla consisted of a destroyer, frigate and supply vessel, which all later entered the East China Sea.

The Defense Ministry said it was continuing to analyze the move while keeping an eye on the warships, which were observed last month sailing off Hokkaido as part of a larger flotilla that was also spotted off Chiba Prefecture and around the Izu Islands south of Tokyo.

Last month, Defense Minister Nobuo Kishi lambasted what he called a “show of force,” with warships nearly circumnavigating Japan.

Moscow said last month that 40 of its warships were participating in large-scale military exercises in the Pacific Ocean, but it was not clear if the three vessels were taking part in those drills.

The Russian military has ramped up its activities in the region in the months since its invasion of Ukraine in late February, including apparent joint exercises with Chinese forces.

In his first meeting with his Chinese counterpart, Kishi last month expressed “serious concerns” over the Sino-Russian exercises, including repeated military flights near Japanese airspace that he called “a demonstration against Japan.”

According to the Japanese Defense Ministry, the Russian military has used the series of high-profile exercises to highlight its advanced weaponry and ability to operate in both the European and Asian theaters simultaneously amid the war in Ukraine.