The U.S. on Thursday issued new sanctions targeting four Russian officials allegedly involved in the 2020 poisoning of opposition leader Alexey Navalny.

The US Treasury Department identified the sanctioned operatives as Alexey Alexandrovich Alexandrov, Konstantin Kudryavtsev, Ivan Vladimirovich Osipov and Vladimir Alexandrovich Panyaev. Three of the four have worked with a specialized laboratory run by the Russian security service known as the FSB Criminalistics Institute. All four have previously been targeted by U.S. sanctions for acting on behalf of the FSB.