The Moscow-installed deputy head of Ukraine's southern Kherson region, Kirill Stremousov, has died in a car crash, officials said Wednesday.
Stremousov, 45, was one of the highest-profile officials in Ukraine supporting Moscow's offensive.
Stremousov's aide, speaking to AFP, confirmed his death.
"I confirm the death of Kirill Sergeyevich," the aide said, referring to Stremousov by his first name and patronymic.
Kherson's Russian-appointed acting governor, Vladimir Saldo, called his passing "tragic," saying his car got into an accident in the region.
Saldo called Stremousov one of the "brightest" people he has known and said he leaves behind five children, with a sixth due soon.
The head of Russia-annexed Crimea, Sergei Aksyonov, called Stremousov a "true fighter" and a "Russian patriot."
The region's main city, also called Kherson, was the first urban hub to be captured by Russia after President Vladimir Putin sent troops into Ukraine on February 24.
Ukrainian troops are now advancing towards the city and causing heavy losses among Russian troops.
Russian forces have for weeks organised evacuation of Kherson residents to Russia and other Moscow-controlled regions, which Kyiv has condemned as a mass deportation.