The Japanese government is concerned about possible use of nuclear weapons in the Ukraine crisis, the top government spokesman said on Tuesday.

"We are seriously concerned about the possibility of the use of nuclear weapons during Russia's invasion of Ukraine," Chief Cabinet Secretary Hirokazu Matsuno told a news conference.

"We, as a sole country that has suffered nuclear attacks during war, intends to keep on appealing firmly that any threat of the use of nuclear weapons, let alone their actual use, should never be allowed."

(Reporting by Kiyoshi Takenaka, editing by Ed Osmond)