"The Associated Press stands by its story," Kaiser said. "We will defend the lawsuit vigorously."
In March, Jeff Horwitz and Chad Day, writers in the AP local news bureau in Washington, DC, published an article claiming the news agency had obtained information about Manafort's annual contract with Deripaska that was signed in 2006 and is worth $10 million.
The Russian businessman said the claims of his pro-Kremlin agenda were "a lie" and asked through his attorney that AP issue a correction and retraction.
The agency refused the request, leading to Deripaska's lawsuit, in which the billionaire asks for "an appropriate amount in monetary damages."
Russia has repeatedly denied US claims it meddled in the US election process, calling them absurd. Kremlin spokesman Dmitry Peskov said Moscow did not have official contacts with Trump's team during the presidential campaign.