The Czech Republic has alleged Russia was involved in a 2014 ammunition depot explosion, triggering its biggest dispute with Moscow since the end of the communist era.
Late Saturday (April 18), it expelled 18 Russian embassy staff and said investigations linked Russian intelligence to the blast.
Meanwhile, Czech police said they were searching for the two men Britain charged with the Novichok poisoning in the English city of Salisbury in 2018, and said they were in the Czech Republic in the days leading up to the depot blast.
They were wanted in connection with "serious criminal activity", police said, and were carrying passports in the names of Alexander Petrov and Ruslan Boshirov.
Those were the aliases used by the two Russian military intelligence officers accused of the attempted poisoning of former Russian spy Sergei Skripal and his daughter Yulia.
The expulsions and allegations come at a time of heightened Russian-Western tensions.
The Czech Republic is informing its NATO and European Union allies of the allegations and will discuss the matter at an EU foreign ministers' meeting on Monday, acting Foreign Minister Jan Hamacek said on Twitter on Sunday.
The Interfax news agency cited Vladimir Dzhabarov, a senior Russian lawmaker, as saying Prague's claims were absurd and Moscow's response should be proportionate.
Britain's foreign minister, Dominic Raab, said on Sunday the UK stands in "full support" of the Czech Republic, and said the latest allegations have exposed the lengths Russian intelligence services will go to.