NEW YORK — A former CNBC and Fox News employee has been arrested in London for his work as a television producer for a Russian media baron tied to aggression in Ukraine over the past eight years, particularly in Crimea, U.S. prosecutors announced Thursday.

Jack Hanick, 71, also known as “John,” was arrested in London on Feb. 3 in what U.S. Attorney Damian Williams described as the first-ever criminal indictment charging a violation of U.S. sanctions resulting from Russia’s 2014 annexation of Crimea.

Hanick’s lawyers in New York and London didn’t immediately respond to a request for comment. If he is successfully extradited, the sanctions charge carries a potential penalty of up to 20 years in prison.

Williams said Hanick worked for years for Russian oligarch Konstantin Malofeyev — the founder of a Russian Orthodox news channel, Tsargrad TV — even after U.S. sanctions banned U.S. citizens from working for or doing business with him.

“The Justice Department will do everything it can to stamp out Russian aggression and interference,” Assistant Attorney General Matthew G. Olsen said in a news release.

Olsen said that after Malofeyev was sanctioned for threatening Ukraine and providing financial support to the Donetsk separatist region, Hanick “knowingly chose to help Malofeyev spread his destabilizing messages by establishing, or attempting to establish, TV networks in Russia, Bulgaria, and Greece, in violation of those sanctions.”

An indictment returned in Manhattan federal court alleged that Hanick worked directly for and for the benefit of Malofeyev from at least 2013 through at least 2017.

According to his LinkedIn page, Hanick worked as a director for CNBC for over a year in 1995 before joining the Fox News Channel as a director from July 1996 to August 2011. He said he was on the channel’s “start-up team.”

A Fox News spokesperson declined comment. CNBC did not immediately respond to a message seeking comment.

Malofeyev was designated for sanctions in December 2014 by the U.S. Treasury Department, which said he was one of the main sources of financing for Russians promoting separatism in Crimea.

In an October 2015 article in the Financial Times Magazine, Malofeyev, alternatively spelled “Malofeev,” by some English-language news outlets, talked about hiring Hanick to help launch Tsargrad TV because he admired Fox News and wanted to put a “conservative yet modern spin on global news.”

Malofeyev and Hanick met when they were speakers at a Moscow conference on morality in the media. Both are devout Christians.

“He seemed like a very humble guy. I had no idea he had a lot of power or political pull. I’m still not sure what he has,” Maloffeyev told the Financial Times in 2015.

Of Putin, he was quoted as calling him a “a historical leader, the best that Russia has had in 100 years, since before the revolution. We got very lucky.”

Prosecutors said that when FBI agents interviewed Hanick about his work for Malofeyev, he made false statements.

In 2015, Hanick authored an opinion piece for The New York Observer warning that a war between Washington and Moscow was on the horizon and saying Russia’s point of view was largely ignored by Americans.

He defended Russia’s occupation of Crimea, assailed U.S. sanctions as a mistake, praised Putin, castigated NATO and said neither it nor the U.S. could ever win either an economic or military war with Russia.

“Russian history is filled with invaders trying to conquer Russia. Napoléon and Hitler are only the latest examples. Russia has always prevailed,” he wrote.

A note at the end of the piece said Hanick had “recently completed the development of a state of the art television network in Moscow, built without government funding.”