Japan's Prime Minister Kishida Fumio has strongly condemned Russia's recognition of the independence of two breakaway regions in eastern Ukraine.

Kishida told reporters on Tuesday that Russia's action infringes on Ukraine's sovereignty and unity, violates international law and cannot be allowed.

He said Japan will closely watch developments with serious concern and work with other G7 countries and the global community to coordinate responses, including sanctions.

The prime minister said that should Russia invade Ukraine, Japan will also respond while working with the G7 members and the international community.

Kishida said he has been told that some Japanese nationals in Ukraine are leaving, but many others including those who have Ukrainian family members are determined to stay.

He said the government will continue through the Japanese Embassy to call on Japanese nationals to leave, as the situation is becoming increasingly tense.