Since a coalition of Ukrainian opposition groups took control of Independence Square in Kiev and held it long enough to undermine the authority of President Viktor Yanukovych, the Russian government and news media outlets under Kremlin control have consistently focused on the part played by far-right, nationalist demonstrators who manned the barricades there during deadly clashes with the police.

To counter the perception fostered in Moscow that the interim government in Kiev, which took power after Mr. Yanukovych fled the country, is led by neo-Nazis and fascist thugs, pro-Western Ukrainian activists have drawn attention to voices of moderation and tolerance in their coalition. One part of that effort was a YouTube video letter to the Russian people from prominent Ukrainian musicians and artists who appealed, in Russian, for peace, love and understanding from their neighbors. “There are no ‘Nazis’ here; your brothers are here,” the singer Valeriy Kharchyshyn said in the video. “We love you and we don’t want war.”

In that context, a highly discordant note was struck by video posted on YouTube this week that showed three men who represent the Ukrainian nationalist party Svoboda in Parliament berating the head of Ukraine’s state broadcaster over his decision to cover the Kremlin ceremony marking the annexation of Crimea.

The video, which was recorded by one of the Svoboda activists who barged into the office of the television executive, Oleksandr Panteleymonov, on Tuesday, also showed two of the party’s lawmakers, Ihor Miroshnichenko and Bohdan Beniuk, assaulting Mr. Panteleymonov for initially refusing to sign a letter of resignation. After the camera stopped rolling, a battered Mr. Panteleymonov finally agreed to step down.

Hours after the original video was uploaded to YouTube by the Svoboda party spokesman Oleksandr Aronets, it was deleted, but not before multiple copies were made by pro-Russia activists who seized on the clip as evidence that Kiev was now run by the mob rule of dangerous vigilantes. The next day, the most violent portion of the video was subtitled by RT, the Kremlin-funded network.

(Late Thursday, YouTube removed the RT copy of the video, and several others, for violating the copyright of the Svoboda party spokesman, who seems to be working to erase the evidence from the Internet through legal means.)

Journalists, activists and the new prime minister, Arseniy Yatsenyuk, a political ally of Svoboda, reacted with disgust to the self-documented assault.

Such behavior is especially unacceptable in the current situation in #Ukraine //t.co/GQ4lcjASl0 #Svoboda #Kyiv — Olga Rudenko (@olya_rudenko) 19 Mar 14

The party’s official Twitter feed reported Mr. Miroshnichenko’s defense of the group’s actions — he claimed that Mr. Panteleymonov was guilty of treason for broadcasting enemy propaganda in a time of war and could not be called a journalist given the station’s poor reporting on the protest movement. But even the leader of Svoboda, with his own history of inflammatory behavior, called the attack “inappropriate.”

As the English-language Kyiv Post reported in the aftermath of the incident, attention focused on the new prosecutor general, Oleh Maknitskiy, who is also a Svoboda party member and “is now expected to impartially investigate the assault.” One journalist for the Kiev news site Ukrainska Pravda — which saved a copy of the video and published a photograph of the letter of resignation the executive was forced to write — called the decision a moment of truth for the new prosecutor.

Mustafa Nayyem, the Afghan-Ukrainian journalist whose Facebook call for demonstrations helped start the protest movement, also condemned the assault and called for protests outside the prosecutor’s office and in front of the Svoboda party’s headquarters.

On Twitter, Mr. Nayyem seconded another journalist’s suggestion that the footage looked as if it had come from the imagination of the Russian president, Vladimir V. Putin. Mr. Nayyem also retweeted another blogger’s sardonic message that Svoboda members should be considered Kremlin agents, illustrated with an image of Mr. Putin raising his glass, as if in tribute to their work on his behalf.