Two former associates of ex-national security adviser Michael Flynn have been charged with “covertly and unlawfully” trying to influence U.S. politicians to extradite a Turkish cleric from the U.S.

Bijan Kian, 66, and Kamil Ekim Alptekin, 41, were charged Monday with conspiracy to act as agents of a foreign government. Alptekin, a Dutch-Turkish businessman, is also charged with three counts of lying to federal agents.

The scheme involved a secret effort to build support among American politicians to remove from the U.S. the cleric Fethullah Gulen, a longtime target of Turkish President Recep Tayyip Erdogan living in self-imposed exile in Pennsylvania.

"The defendants sought to discredit and delegitimize the Turkish citizen in the eyes of politicians and the public, and ultimately to secure the Turkish citizen's extradition," according to an indictment.

As part of the plot, the defendants used Flynn's firm, the now-dissolved Flynn Intel Group, to damage Gulen's reputation, according to the indictment, which refers to the firm only as Company A.

The pair kept secret that the work was in fact directed by the Turkish government, federal prosecutors said.

The scheme included using a Dutch company owned by Alptekin, Inovo, to appear to be the “client” of Flynn's firm and pay the fee of $600,000 in three installments, according to the indictment.

Alptekin made the payments to Flynn's firm from an account in Turkey.

"The indictment alleges that after Alptekin made the payments to Company A, it was to kick back 20 percent of the payments to Alptekin’s company in the Netherlands, and two such kickbacks were made," the Justice Department said in a statement.

NBC News reported last November that federal investigators were zeroing in on Kian, an Iranian-American who was a partner at the now-dissolved Flynn Intel Group, for his role in the failure of the firm to disclose its work on behalf of foreign governments.

Flynn pleaded guilty in December 2017 to a charge of lying to the FBI about his conversations with Russian ambassador Sergey Kislyak in the weeks before President Donald Trump took office. He has been cooperating with investigators.

The charges against Kian and Alptekin came the day before Flynn is due to be sentenced in federal court. Special Counsel Robert Mueller's team has argued that he should receive a light sentence in exchange for his cooperation.