Moscow announced Monday it was expelling a Ukrainian embassy worker, the latest in a wave of diplomatic expulsions that have embroiled Russian and European diplomats.
The expulsion came amid heightened tensions between Moscow and Kiev over an uptick in fighting between Ukraine's army and pro-Russia separatists in eastern Ukraine.
Russia's foreign ministry said in a statement that due to "unfriendly actions taken by the Ukrainian side [...] an employee of the Ukrainian embassy in Russia was declared persona non grata."
It added that the diplomat, who was not named, must leave Russia by the end of April.
The ministry warned Ukraine that further measures would be taken against embassy staff in Moscow "in the event of continuing hostile actions" against Russian diplomats in Ukraine.
The move came after Ukraine last week expelled a Russian diplomat in response to Moscow's order for a Ukrainian consul in Russia's second city Saint Petersburg to leave the country.
According to Russia's security agency, the consul was trying to obtain sensitive information from a Russian national.
Recent weeks have seen a wave of expulsions of Russian officials from European countries and the United States over claims of hacking and espionage.
Romania on Monday said it was removing a Russian diplomat in solidarity with the Czech Republic, which recently ordered out 18 Russian embassy staff over a deadly explosion at an ammunition depot in 2014.
Russia earlier Monday expelled an Italian naval attache responding to a similar move by Rome last month in the fallout of a spying scandal.
Kiev has been fighting pro-Russia separatists in its eastern breakaway regions since 2014, following Moscow's annexation of the Crimean peninsula.
At least 31 Ukrainian soldiers have been killed since the start of the year, compared to 50 in all of 2020, while the separatists say 22 of their fighters have died.