NEW YORK—An attack on Thursday against the acclaimed writer Ludmila Ulitskaya and others attending an awards ceremony for high school students is an appalling demonstration of disrespect for even the most basic free expression rights in Russia today, PEN America said Friday.

Ulitskaya was doused with a green disinfectant by young men who also hurled eggs and shouted obscenities to disrupt the event, sponsored by human rights organization Memorial, that brought students from across the country to Moscow to honor the winners of an essay contest on 20th Century Russian history. Some among the assailants wore World War II-era uniforms, and the group hoisted a replica of the Soviet Victory flag and held placards reading, “We don’t need alternative history.”

The 73-year-old Ulitskaya, who led a PEN America delegation of Russian literary figures to the United States in January, has stood as a forceful advocate for free expression despite the rising risks of dissent under Russian President Vladimir Putin. Memorial, a Russian human rights organization with a long and admirable record of exposing Soviet-era political terror, was declared in 2014 to be a “foreign agent’’ under a Russian law that requires organizations that accept funds from abroad to register and is designed to pressure independent civil society groups.

“The right to understand and debate history and to protect it from distortion for political ends is fundamental to any open society,’’ said Dru Menaker, Director of International Partnerships at PEN America. “To seek to discourage schoolchildren from participating in an event that engages them as citizens certainly teaches them a very disturbing lesson in repression.’’

PEN America called on Russian authorities to investigate and prosecute the attackers. News reports said a spokesman for the nationalist, pro-Kremlin National Liberation Movement acknowledged picketing the event but denied its members were involved in the assault.

In Discourse in Danger: Attacks on Free Expression in Putin’s Russia released in January, PEN America documented the Russian government’s campaign to constrain free expression by limiting public access to information, closing avenues of civic engagement, and populating discourse with approved ideas. While in New York and Washington earlier this year, Ulitskaya and her fellow writers drew special attention to the active re-writing of Russian history that has become part of this repression of independent thought.

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PEN America stands at the intersection of literature and human rights to protect open expression at home and abroad. We champion the freedom to write, recognizing the power of the word to transform the world. Our mission is to unite writers and their allies to celebrate creative expression and defend the liberties that make it possible. www.PEN.org