A group of 10 naval vessels from China and Russia sailed through a strait separating Japan’s main island and its northern island of Hokkaido on Monday, the Japanese government said, adding that Tokyo is closely monitoring such activities.

Then on Tuesday, there were fresh tensions in Japan as North Korea fired what appeared to be a submarine-launched ballistic missile (SLBM) off its east coast, South’s military said, pulling Japan’s new Prime Minister Fumio Kishida off an election campaign trail and also overshadowing the opening of a major arms fair in Seoul.

The Chinese-Russian sail-through was the first time Japan confirmed the passage of naval vessels from these two countries passing down the Tsugaru Strait, which separates the Sea of Japan from the Pacific.

While the strait is regarded as international waters, Japan’s ties with China have been plagued by conflicting claims over a group of tiny East China Sea islets.

That apart, Tokyo has a territorial dispute with Moscow.

“The government is closely watching Chinese and Russian naval vessels’ activities around Japan like this one with high interest,” deputy chief cabinet secretary Yoshihiko Isozaki said. “We will continue to do our utmost in our surveillance activity in waters and airspace around Japan.”

Russia and China held joint naval drills in the Sea of Japan from October 14-17 involving warships and support vessels from Russia’s Pacific fleet. Moscow and Beijing have cultivated close military ties in recent years at a time when their relations with the West have soured.

North Korea’s latest missile launch, meanwhile, saw the US military’s Indo-Pacific Command condemning it as destabilising. South Korean and US officials were investigating if the missile was a previously unseen version displayed last week at an exhibition in Pyongyang, a South Korean source told Reuters.

They were studying if the missile was fired from North Korea’s experimental Gorae-class submarine, he added.