"We believe this was a show of force toward Japan", Kishi said at a press conference, as cited by Kyodo.
Kishi also noted that the incident "clearly demonstrates the increasingly severe security environment surrounding Japan".
On his part, Japanese Foreign Minister Toshimitsu Motegi said on Tuesday that Tokyo had expressed its concern to Russia and China about their actions.
"With regards to a passage of Tsugaru and Osumi straits by Russian and Chinese simultaneously, this is the very first time that we're experiencing this and activities by the navy vessels of China and Russia in the seas around Japan is something that we are watching very closely with high interest and we have expressed our concerns through diplomatic channels to both the Chinese and the Russian side. We will continue to monitor the situation", the minister said.
Motegi also noted that concerning Russia, in addition to the issue of the ships' passage, there are other unresolved problems.
"There are various issues such as territorial issues that we need to negotiate. And the fact that the negotiations will go on has been agreed", he added.
A group of naval vessels from China and Russia sails during joint military drills in the Sea of Japan, in this still image taken from video released on October 18, 2021. Video released October 18, 2021
© REUTERS / RUSSIAN DEFENCE MINISTRY
On Saturday, Russian and Chinese warships conducted the first joint patrol in the Pacific Ocean, with the vessels traversing the international waters of the Tsugaru Strait in the Sea of Japan.
Tokyo, in turn, said that the warships also sailed through the Osumi Strait and the Japanese military registered a helicopter taking off from and landing on the deck of a Chinese destroyer near the Danjo Islands. In response, the Japanese Air Self-Defenсe Force scrambled its fighter jets.