Stremousov, who acted as the deputy governor in Kherson, was killed in "a car crash", the governor's office stated.

Stremousov was one of the most vocal proponents of Russia's full-scale invasion of Ukraine in late February. He has been wanted for treason by the Ukrainian authorities since his appointment two months into the invasion.

"Kirill Stremousov perished. This is a huge tragedy, an irreparable loss," Sergei Aksionov, the Kremlin-installed leader of Crimea, said on Telegram.

Kherson is one of the four regions — together with Donetsk, Luhansk and Zaporizhzhia — illegally annexed by Moscow on Sept. 30 after sham referendums were held on their independence from Ukraine.

Stremousov's death came as Russia-backed authorities in Kherson are said to be likely beginning a new phase of "evacuations" from the city, according to the US-based Institute for the Study of War. Kyiv has called them "forced deportations".

Stremousov has been active on social media in recent days, imploring the residents of the region to leave for Moscow-held territories. He said earlier that Nov. 7 would be the last day of centrally-organized evacuations from Kherson city.

Meanwhile, Russian soldiers continue to dig in around the city, with Ukrainian forces inching closer as their offensive in the region moves forward.

Kherson is the only regional capital of Ukraine that Moscow captured since the February invasion.