Russia's Defence Ministry said Tuesday that its navy had fired test anti-ship missiles at mock targets in the Sea of Japan during military exercises.
Russia's Pacific Fleet drills came a week after Tokyo's Prime Minister Fumio Kishida visited Ukraine.
Moscow holds regular naval drills off its Pacific coast, but Tokyo said these had been "increasing" and that it was "closely" monitoring Russian military activity in the area.
"In the waters of the Sea of Japan, missile boats of the Pacific Fleet fired Moskit cruise missiles at a mock enemy sea target," the Russian Defence Ministry said on Telegram early on Tuesday, adding that two ships had taken part in the exercise.
"The target, located at a distance of about 100 kilometers, was successfully targeted by a direct hit from two Moskit cruise missiles."
Moscow said its naval aviation oversaw the "safety of the combat exercise."
Russia has held such exercises before, firing test Moskit missiles in a similar drill last year.
But Japanese Foreign Minister Yoshimasa Hayashi said that as Moscow's Ukraine offensive continues "the Russia military is increasing its activity in the Far East, including areas near Japan."
"We will continue to monitor Russia's military movements closely," he said in comments reported by the Jiji Press news agency.
He said there had been no reported damage from the test strikes.
Last week, Russia said two of its Tu-95 strategic bomber planes performed "flights in the airspace over neutral waters in the Sea of Japan."
Japan has joined Western allies in sanctioning Russia over its offensive in Ukraine, and the bomber jet flights came after Kishida visited Kyiv to meet with Ukrainian leader Volodymyr Zelensky.