On Saturday, Prague kicked out 18 Russian diplomats after accusing Russia of being behind an attack on an ammunition depot. On Sunday, Moscow retaliated.
The expulsions will most likely decimate the Czech diplomatic presence in Russia, where the Czechs maintain only several dozen diplomats.
By contrast, the Russian Embassy in Prague, the Czech capital, is believed to be one of the countrys largest in Europe and is used, security experts say, as a staging area for intelligence operations carried out in a number of Western countries.
The 2014 explosions, first in the village of Vlachovice and then, two months later, at a nearby ammunition depot, were never fully explained, though at the time authorities raised the possibility of sabotage. Two workers at the government-owned depot were killed.
The blasts came at a time when Ukrainian forces were desperate for weapons to beat back gains made by Russian-backed separatists, as well as when Russian forces were deepening their involvement in the Syrian civil war.
On Saturday, the Czech prime minister, Andrej Babis, announced that a subsection of Russias military intelligence agency known as Unit 29155 was responsible for the explosions.