VILNIUS, Lithuania (AP) — The three Baltic countries on Friday ordered the expulsion of a total of four Russian diplomats as an act of solidarity with the Czech Republic, where scores of diplomats have been expelled since Saturday over the alleged involvement of Russian spies in a massive ammunition depot explosion in 2014.

Lithuanian Foreign Minister Gabrielius Landsbergis said two embassy staff had been declared persona non grata “because they had carried out activities incompatible with their diplomatic status.” They were given seven days to leave Lithuania.

On Twitter, the Estonian Foreign Ministry said its single expulsion was related to the the 2014 explosion, saying it “violates international law, undermines European security & stability and is unacceptable.” Latvian Foreign Minister Edgars Rinkevics said that Latvia has decided to expel a Russian diplomat because the country “will not tolerate subversive activities on its soil or that of its partners and allies.”

On Thursday, the Czech Republic ordered 63 more Russian diplomats to leave the country after previously expelling 18 whom it had identified as spies in a case related to the huge blast.

Estonia, Lithuania and Latvia — all former Soviet republics — broke away from the Soviet Union three decades ago and joined NATO and the EU in 2004. They are among the Kremlin’s harshest critics.