(Reuters) - U.S. President Donald Trump’s former campaign chairman Paul Manafort agreed to cooperate with Special Counsel Robert Mueller’s investigation of Russian meddling in the 2016 U.S. election as part of a plea deal, prosecutors said on Friday.

FILE PHOTO: Republican presidential nominee Donald Trump gives a thumbs up as his campaign chairman Paul Manafort looks on during Trump's walk through at the Republican National Convention in Cleveland, U.S., July 21, 2016. REUTERS/Rick Wilking/File Photo

Manafort, 69, pleaded guilty in federal court in Washington to two criminal counts, becoming the most prominent former Trump campaign official to strike a plea deal in Mueller’s investigation.

Trump has denied any collusion with Russian officials by his campaign and has long denounced the investigation as a political witch hunt. Moscow denies U.S. intelligence agency allegations that it interfered in the political process.

(The court documents related to Mueller's investigation are at www.justice.gov/sco)

Mueller told Trump’s attorneys in March he was continuing to investigate the Republican president but did not consider him a criminal target “at this point,” the Washington Post reported in early April.

The following is a list of people who have been indicted or convicted or are being investigated:

** On Sept. 7, George Papadopoulos, a former campaign adviser to Trump, was sentenced to 14 days in prison. He had pleaded guilty in October to lying to FBI agents about the timing and significance of his contacts, including a professor who told him the Russians had “dirt” on Trump’s Democratic presidential rival, Hillary Clinton.

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According to documents released with his guilty plea, Papadopoulos offered to help set up a meeting with then-candidate Trump and Russian President Vladimir Putin.

** On Aug. 31, Samuel Patten, 47, an American who is the business partner of a Russian national accused by the special counsel’s office of having ties to Russian intelligence, pleaded guilty to unregistered lobbying for a pro-Kremlin political party in Ukraine. He also agreed to cooperate with investigators.

** On Aug. 21, Trump’s former personal lawyer Michael Cohen pleaded guilty in federal court in New York to campaign finance violations and other charges, saying he made payments to influence the 2016 election at the direction of a candidate for federal office. The deal included a possible prison sentence of up to five years and three months.

** Also on Aug. 21, a jury in federal court in Alexandria, Virginia, found former Trump campaign chairman Manafort guilty on eight of 18 charges of filing false tax returns, failing to disclose his offshore bank accounts and bank fraud. The judge declared a mistrial on the remaining 10 counts, which were dismissed as part of Manafort’s plea deal on Sept. 14 in a second case against him in Washington.

** Michael Flynn, a former national security adviser to Trump who was also a close campaign aide, pleaded guilty in December to lying to FBI agents about his contacts with Russia and agreed to cooperate with Mueller’s investigation. Mueller and Flynn’s defense team last month asked for more time before Flynn is sentenced.

** Rick Gates, a former deputy campaign chairman for Trump, pleaded guilty in February to conspiracy against the United States and lying to investigators, and agreed to cooperate with the Mueller investigation.

** Alex Van der Zwaan, a lawyer who once worked closely with Manafort and Gates, pleaded guilty in February to lying to Mueller’s investigators about contacts with an official in the Trump election campaign. Van der Zwaan, the Dutch son-in-law of one of Russia’s richest men, was sentenced on April 3 to 30 days in prison and fined $20,000.

** Twelve Russian intelligence officers were indicted by a federal grand jury on July 13, accused of hacking Democratic Party computer networks in 2016, in the most detailed U.S. accusation yet that Moscow meddled in the presidential election to help Trump. The Russian government has repeatedly denied meddling in the election.

** Thirteen Russians and three Russian entities were indicted in Mueller’s investigation in February, accused of tampering in the 2016 election to support Trump.

** Richard Pinedo, who was not involved with the Trump campaign, pleaded guilty in a case related to the Mueller probe in February to aiding and abetting interstate and foreign identity fraud by creating, buying and stealing hundreds of bank account numbers that he sold to individuals to use with large digital payment companies. Pinedo “made a mistake” but “had absolutely no knowledge” about who was buying the information or their motivations, his lawyer said. Sources familiar with the indictment said Pinedo was named as helping Russian conspirators launder money as well as purchase Facebook ads and pay for rally supplies.

** Konstantin Kilimnik, a Manafort aide in Ukraine and political operative with alleged ties to Russian intelligence, was charged on June 8 with tampering with witnesses about their past lobbying for Ukraine’s former pro-Russian government.