The Czech Republic and Russia have kicked out dozens of each others' diplomats in what's now become their biggest dispute since the end of the communist era.
The Czech Republic ordered eighteen Russian diplomats to leave within 72 hours after linking Russian spies to a 2014 explosion at an arms depot Southeast of Prague.
On Sunday, Moscow in turn kicked out 20 Czech diplomats.
Prague says it's told NATO and the EU that it believes Russia was behind the explosion years ago and EU foreign ministers are set to discuss the matter on Monday.
Czech police say that days before the explosion, two men using the names Alexander Petrov and Ruslan Boshirov had travelled to the Czech Republic.
Those two names are also aliases connected to 2018 poisonings in Britain of former Russian spy Sergei Skripal and his daughter.
Russia has called Prague's allegations absurd, since Czech authorities previously blamed the blast on the depot's owners.
It also accused Prague of "striving to please the United States against the backdrop of recent U.S. sanctions against Russia."
Meanwhile the U.S. State Department commended Prague's firm response to "Russia's subversive actions on Czech soil."