Czech police detained five people Wednesday on suspicion of engaging in terrorist activities in Eastern Ukraine.

They were accused of fighting for pro-Russian groups, according to the Chief Prosecutor’s Office in Prague.

The five nationals were members of an armed organization and had relations with Russia’s Main Intelligence Directorate (GRU), according to local media.

On April 18, the Czech Republic expelled 18 Russian diplomats for alleged links to explosions at two warehouses in 2014 which prompted large-scale evacuations.

They included an explosion at an ammunition depot in the village of Vrbetice in the Zlin region of the Czech Republic that left two people dead and a second explosion at a nearby depot.

In a tit-for-tat move, Russia announced Sunday that it was expelling 20 Czech diplomats.

Czech Foreign Minister Jakub Kulhanek called on Russia to review its decision, adding that otherwise the Czech Embassy in Moscow would not be able to continue its activities./aa