The Associated Press has led in-depth coverage of the lobbying and PR activity of Donald Trump's campaign chairman Paul Manafort, who advocated for pro-Russian interests in the Ukraine without registering in the US as a foreign agent.

Manafort resigned today from the Trump campaign.

paul manafortThe AP reported Thursday that the efforts of Manafort and his deputy Rick Gates included plays for positive press coverage of Ukrainian officials in major media like the New York Times and Wall Street Journal, with the dual goal of "undercutting American public sympathy for the imprisoned rival [Yulia Tymoshenko] of Ukraine's then-president."

According to the New York Times, $12.7M in undisclosed cash payments were designated for Manafort from the pro-Russian political party of former president Viktor Yanukovych. Ukrainian investigators allege the payments were part of an illegal payment sysytem involving election officials, the Times reported.

Manafort in a statement accused the Times of fostering a "political agenda" and attacking "my character and reputation rather than present an honest report." He called himself a "campaign professional" who works in the US and overseas and denied ever accepting cash payments. He also denied ever working for the governments of Ukraine or Russia.

In a campaign shakeup earlier this week amid the Ukraine reports and scrutiny, as well as a flagging campaign, Trump replaced Manafort as campaign manager but let him stay on as chairman. Trump said today: "This morning Paul Manafort offered, and I accepted, his resignation from the campaign. I am very appreciative for his great work in helping to get us where we are today, and in particular his work guiding us through the delegate and convention process. Paul is a true professional and I wish him the greatest success."

Manafort has said the work did not require registration under the Foreign Agent Registration Act in the US.

The AP reported that Manafort's deputy, Gates, personally directed the work of Washington lobbying shops Mercury and Podesta Group from 2012-14, organizing meetings between US and Ukrainian officials.

Yahoo chief investigative correspondent Michael Isikoff reported Mercury senior partner Vin Weber was recruited by Manafort to lobby for a Brussels non-profit, European Centre for a Modern Ukraine, backed by unnamed business people. Weber told Isikoff he repeatedly asked Manafort to disclose the principals, but Manafort declined.

Manafort also hit the Times for not highlighting the Clinton Foundation's receipt of funds "in exchange for favors from Hillary Clinton while serving as Secretary of State."