"We are ready to take action, also at EU level as appropriate, and discussions on this continue among member states," an EU official told.
Poland is expected to expel Russian diplomats this week, EU diplomatic sources said. Bulgaria and Romania might also follow, they added.
The Baltic states and Slovakia have led the way, expelling seven Russians in total last week.
As a reminder, the Minister of Foreign Affairs Jan Hamacek decided to expel from the Czech Republic 18 Russian diplomats who are suspected of work for special services of the Russian Federation. The Russian GRU officers were charged with involvement in an ammunition explosion in the village of Vrbetice in 2014. The explosion led to numerous destructions and the deaths of two locals. Only 6.5 years later, the Czech government officially accused Russia of organizing this sabotage.
Russian Foreign Ministry spokeswoman Maria Zakharova called the decision of the Czech authorities to expel 18 diplomats from the country a "trick" and promised a response from Moscow. Then, The Russian Foreign Ministry decided to expel 20 Czech diplomats from Moscow.