WASHINGTON (REUTERS) - US President Donald Trump's re-election campaign sued CNN for libel on Friday (March 6), over an opinion piece that said the campaign had left open the possibility of seeking Russia's help in the 2020 election.

The libel lawsuit was the campaign's third in 10 days against major media outlets, following cases against the New York Times and the Washington Post.

All three lawsuits focused on opinion pieces published in 2019 that, according to the campaign, suggested it has had improper ties with Russia.

CNN had no immediate comment.

A person familiar with the matter said CNN had yet to review the lawsuit.

CNN is a unit of AT&T.

The lawsuits each seek millions of dollars in damages, and extend the Republican president's years-long battle with news media he believes demonstrate bias against him.

Friday's lawsuit objected to a statement in a June 13, 2019 opinion piece by CNN contributor Larry Noble, which referred to Special Counsel Robert Mueller's report on Russian interference in the 2016 US election.

Noble wrote: "The Trump campaign assessed the potential risks and benefits of again seeking Russia's help in 2020 and has decided to leave that option on the table."

The campaign said CNN was "well aware" that the statement was untrue when published, and the piece reflected its "systematic pattern of bias" against the campaign.

Trump's campaign used identical language in its lawsuits against the Times and Post.