European Union foreign ministers are to discuss on Monday Russia's undercover military operations in Europe after a 2014 espionage operation was linked to the poisoning of former spy Sergei Skripal in England.
The Czech Republic announced on Saturday it was expelling 18 Russian diplomats over a blast at a munitions depot as it searched for two men carrying passports in the names of two suspects in the Skripal case.
They were the aliases of the military intelligence officers who British prosecutors charged with the poisoning of Mr Skripal and his daughter Yulia with the nerve agent Novichok in the English city of Salisbury in 2018. Dawn Sturgess, 44, died after inadvertently spraying herself with Novichok contained in a discarded perfume bottle.
The UK has accused Russia of orchestrating the poisoning. Russia denies involvement.
Czech Prime Minister Andrej Babis said the expulsions were based on “unequivocal evidence” provided by Czech intelligence and security services that indicated the involvement of Russian military agents in the explosion that killed “two innocent fathers”.
“The Czech Republic is a sovereign state and must adequately react to those unprecedented findings,” Mr Babis said.
The two identified men were in the country in the days leading up to the 2014 explosion.
Interior Minister Jan Hamacek, who is also serving as the country’s Foreign Minister, said the 18 embassy staff were clearly identified as spies from the Russian intelligence services known as GRU and SVR, and were ordered to leave the country within 48 hours.
The explosion took place on October 16, 2014, in a depot in the town of Vrbetice, where 50 tonnes of ammunition was stored. Another explosion of 13 tonnes of ammunition occurred at the depot two months later.
A number of villages were evacuated after the blasts.
The EU's executive commission confirmed remarks by Mr Hamacek on Twitter that the dispute would be addressed during a previously scheduled EU foreign ministers' video conference on Monday.
Dominic Raab, the British Foreign Secretary, said the UK gave its full support to the Czechs after the "reckless and dangerous" attack in 2014.
The blast, he said, exposed the lengths that the Russian intelligence services will go to in their attempts to conduct dangerous and malign operations in Europe.
"This shows a pattern of behaviour by Moscow, following the Novichok attack in Salisbury."
Jennifer Bachus, charge d'affaires at the US embassy in Prague, said her country stood "with its steadfast ally, the Czech Republic".
“We appreciate their significant action to impose costs on Russia for its dangerous actions on Czech soil.”
The Czech announcement came two days after the US said it was expelling 10 Russian diplomats and imposing sanctions against several dozen people and companies, holding the Kremlin accountable for interference in last year's presidential election and the hacking of federal agencies.
Russian Foreign Ministry spokeswoman Maria Zakharova said her country would respond to the Czech decision.
"Prague is well aware of what will follow such tricks," Ms Zakharova told the RIA Novosti news agency.