A Belarusian national has been detained in Poland on suspicion of ordering the attack on Russian opposition leader and Alexei Navalny ally Leonid Volkov on behalf of Moscow, Polish Prime Minister Donald Tusk said Friday. The arrest follows the earlier detention of two Polish nationals.

"A Belarusian working for Russians who ordered two Poles to assassinate Navalny's associate – detained. The attackers are also in custody," the prime minister wrote on Twitter.

Earlier in the day, authorities in Lithuania said they had detained two Polish citizens suspected of carrying out the March 12 attack outside Volkov's home in the Lithuanian capital Vilnius, where he lives in exile.

"Two people have been detained in Poland on suspicion of attacking Russian opposition leader Leonid Volkov," Lithuanian President Gitanas Nauseda was quoted as saying by the U.S. news agency AP.

Niedoszły zamachowiec na prezydenta Zelenskiego, Polak działający w porozumieniu z rosyjskimi służbami - aresztowany 2 dni temu. Białorusin pracujący dla Rosjan, który zlecił dwóm Polakom zamach na współpracownika Nawalnego - zatrzymany. Zamachowcy też już w areszcie. Powiązani…

— Donald Tusk (@donaldtusk) April 19, 2024

He added: "I thank the Republic of Poland for the excellent work done. I discussed the matter with the Polish president [Andrzej Duda] and thanked him for the great cooperation."

Volkov, for his part, thanked the Lithuanian president and law enforcement on Twitter, stressing the "enormous importance to investigate and to expose all the chain-of-command from [Vladimir] Putin to the guy with the hammer."

Thanks a lot, Mr. President.
And great thanks to Lithuanian and Polish law enforcement agencies for the tremendous work they’ve done.

It is of enormous importance to investigate and to expose all the chain-of-command from Putin to the guy with the hammer. https://t.co/Yai5DLqEN3

— Leonid Volkov (@leonidvolkov) April 19, 2024

An assailant smashed a window of Volkov's car, sprayed tear gas into his eyes and hit him with a hammer, police said at the time. The man, who suffered a broken arm and was hospitalized, accused the Russian president of ordering the attack and vowed to continue his opposition work.

The incident came less than a month after the unexplained death in custody of Navalny, who had been imprisoned in a remote Arctic penal colony.

Navalny, who died aged 47, was Russia's best-known opposition figure and Putin's fiercest critic. He had been in custody since January 2021, serving a nine-year sentence for extremism that was widely seen as politically motivated.

Navalny's widow, Yulia Navalnaya, has vowed to continue her husband's work, although she admitted that the attack on Volkov had prompted her to hire a bodyguard.

Volkov was in charge of Navalny's regional offices and election campaigns. Navalny ran for mayor of Moscow in 2013 and tried to challenge Putin in the 2018 presidential election.

Read Also: Two suspects in attack on Navalny ally in Lithuania detained in Poland (in Portuguese)