Ukraine's foreign ministry called out HBO in an X post Wednesday ... asking if it was right for the outlet to work with a person who supports genocide and violates international law.

A quick rundown on the uproar: Biković's been accused of supporting Russia's ongoing invasion of Ukraine ... even posting an X poll showing that trust in Putin was higher than in Ukraine President Volodymyr Zelensky.

He's starred in a string of Russian films, such as 2014's "Sunstroke" ... which Ukraine's Ministry of Foreign Affairs said he'd filmed in Crimea, the peninsula Russia seized from Ukraine in 2014.

In 2018, Putin awarded Biković a Pushkin medal for advancing Russian culture. A year later, Ukraine banned him from entering the country for national security reasons.

The 36-year-old was unfazed over the ban, making it clear where his loyalties lie as he gushed over receiving Russian citizenship in 2021 ... and added, he'd been actively participating in Russian cultural life for more than 7 years.

His casting in the third season of Mike White's anthology series was announced earlier this month ... and production is set to begin next month in Thailand.

Deadline reports he'll likely play a Russian-speaking wellness guru at the hotel -- though his character details haven't been confirmed.

The dark comedy has been a massive hit with fans and has dominated award season with its first 2 seasons ... so expectations are undoubtedly high for the third.