The Russian Justice Ministry on Friday described prominent Kremlin critics, including documentary filmmaker Yuri Dud and political scientist Ekaterina Schulmann, as "foreign agents."

The ministry said in a statement that it had added to its growing list of "foreign agents" nine individuals including 35-year-old Dud, Schulmann, 43, and caricaturist Sergei Yelkin, 59.

Also on the list are now prominent journalists Roman Dobrokhotov, 38, and Karen Shainyan, 40.

Dobrokhotov is the founder of investigative news website The Insider, while Shainyan is an openly gay editor, producer and gay rights activist.

Schulmann, one of Russia's most-quoted political analysts, recently left the country to conduct scientific work in Germany. She told Agence France-Presse (AFP) she had long expected to be designated a "foreign agent."

"And why only now?" tweeted Dobrokhotov in reference to his designation.

Moscow has stepped up efforts to stamp out dissent after President Vladimir Putin sent troops to Ukraine on Feb. 24.

Independent media outlets have been shut down or suspended operations, and tens of thousands of Russians have left the country in protest over the Kremlin's policies.

By law, individuals or entities identified as "foreign agents" must disclose sources of funding, undergo audits and accompany all their texts, videos and social media posts with a caption mentioning content from a "foreign agent."

The status is reminiscent of the Soviet-era term "enemy of the people" and is meant to apply to people or groups that receive funding from abroad and are involved in any kind of "political activity."