Japan on Tuesday ordered the Russian consul in the northern city of Sapporo to leave the country within six days in retaliation for Moscow’s expulsion of a Japanese diplomat last month for alleged espionage.

Japanese Foreign Minister Yoshimasa Hayashi said his ministry declared the consul a persona non grata, or an undesirable person, and ordered him to leave by next Monday. The ministry did not release the consul’s name, but said the step was “conducted as an appropriate measure in response to the measures taken by Russia.”

Hayashi said Vice Foreign Minister Takeo Mori summoned Russian Ambassador to Japan Mikhail Galuzin to inform him of the decision.

Last month, Russia detained the Japanese consul in Vladivostok over espionage allegations and expelled him. The consul, Tatsunori Motoki, returned to Japan last week.

Japanese officials say Motoki was blindfolded and physically restrained while he was detained and interrogated over alleged spying. He was ordered to leave the country within 48 hours. Japan has denied the allegations.

Hayashi has called Russia’s treatment of Motoki a clear violation of international law.

The dispute is the latest example of worsening ties between the two countries following Japan’s imposition of sanctions against Russia for its invasion of Ukraine. Japan and Russia have each expelled a number of diplomats, and Russia has halted peace negotiations with Japan that include talks on islands seized by the Soviet Union at the end of World War II.

Last week, Prime Minister Fumio Kishida condemned Russia’s annexation of parts of Ukraine and said Japan plans to impose more sanctions against Moscow.