Russia has announced that 20 diplomats from the Czech Republic will be expelled from the country.
The Czech Republic expelled 18 Russian diplomats on Saturday.
Czech local intelligence agents say the diplomats are Russian intelligence operatives. They are suspected of involvement in an explosion at an arms depot in 2014 which killed two people.
European Union foreign ministers are set to discuss the accusation during a meeting on Monday.
Moscow has given the Czech diplomats a day to leave while the Czech Republic has given the Russians 72 hours.
Russia’s foreign ministry called the Czech decision “unprecedented” and a “hostile act”.
“In their desire to please the United States against the background of recent US sanctions against Russia, Czech authorities in this respect even outdid their masters from across the pond,” said a foreign ministry statement.