Paul Manafort AP Photo/Mary Altaffer WASHINGTON (AP) — A Russian billionaire close to President Vladimir Putin said Tuesday he is willing to take part in U.S. congressional hearings to discuss his past business relationship with President Donald Trump's former campaign chairman, Paul Manafort.

Last week, The Associated Press reported that Manafort had written aluminum magnate Oleg Deripaska in 2005, proposing to do work for Deripaska that would "benefit the Putin Government." The story was based on interviews with people familiar with Deripaska's business dealings with Manafort and documents obtained by the AP, including strategy memoranda, contracts and records showing international wire transfers for millions of dollars.

In a quarter-page advertisement in Tuesday's editions of The Washington Post and The Wall Street Journal, Deripaska said he was "ready to take part in any hearings conducted in the US Congress on this subject in order to defend my reputation and name."

Manafort signed a $10 million contract in 2006 that laid out a four-country communications and political strategy intended to support Deripaska's company and undermine anti-Russian political movements. Payments continued until at least 2009, seven years before Manafort joined and led Trump's 2016 campaign, according to people familiar with the relationship. They spoke on condition of anonymity because they were not authorized to discuss the business arrangement openly.

In his newspaper ads responding to the AP's story, Deripaska said he never signed "a $10 million contract 'to greatly benefit the Putin Government' with Paul Manafort."

"I have never made any commitments or contracts with the obligation or purpose to covertly promote or advance 'Putin's Government' interests anywhere in the world," Deripaska wrote.

The AP's story said that Manafort wrote a strategy memo proposing that the work he would do for Deripaska would "benefit the Putin Government," not that the contract contained that language.

"This AP Exclusive report falls into the negative context of current US-Russian relations and causes fresh unfair and unjustified concerns and alarm in the US Congress about Russian involvement in US domestic affairs," Deripaska's ad says.

The AP stands by its reporting, spokeswoman Lauren Easton said.

The revelations about Manafort come as Trump campaign advisers are the subject of an FBI probe and two congressional investigations, and they appear to guarantee that Manafort will be sought as a key witness in upcoming hearings. He has volunteered to appear.

Investigators are reviewing whether the Trump campaign and its associates coordinated with Moscow to meddle in the 2016 campaign. Manafort has dismissed the investigations as politically motivated and misguided. The documents obtained by AP show Manafort's ties to Russia were closer than previously revealed.

Russian metals magnate Oleg Deripaska attends a meeting of Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan with businessmen in the Konstantin palace outside St. Petersburg, Russia, Tuesday, Aug. 9, 2016. AP Photo/Alexander Zemlianichenko Deripaska is one of Russia's wealthiest men. He amassed his fortune under Putin and has bought assets abroad in ways widely perceived to benefit the Kremlin's interests. U.S. diplomatic cables from 2006 described him as "among the 2-3 oligarchs Putin turns to on a regular basis" and "a more-or-less permanent fixture on Putin's trips abroad."

A spokesman for Manafort has confirmed that Manafort worked for Deripaska representing him on business and personal matters, but has denied that the work involved "representing Russia's political interests." White House spokesman Sean Spicer said last week that Trump was not aware of Manafort's work for Deripaska a decade ago.

The AP reported last week that Manafort proposed an ambitious political strategy in a June 2005 memo that was based on work he had done in Ukraine. Manafort described how his plan could be used to influence politics, business deals and news coverage inside the United States, Europe and former Soviet republics to the benefit of the Russian government.

"We are now of the belief that this model can greatly benefit the Putin Government if employed at the correct levels with the appropriate commitment to success," Manafort wrote in the 2005 memo to Deripaska. The effort, Manafort wrote, "will be offering a great service that can re-focus, both internally and externally, the policies of the Putin government."

Manafort wrote that the plan would bolster the legitimacy of governments friendly to Putin and undercut anti-Russian figures through political influence campaigns, nonprofit front groups and media operations.

The $10 million contract Manafort signed in 2006 outlined the political and communications activities in Uzbekistan, Tajikistan and Georgia in more detail, but the AP noted last week that the work actually performed is unclear.

Manafort and Deripaska had a falling out laid bare in 2014 in a Cayman Islands court. The dispute involved a nearly $19 million investment that Manafort was orchestrating for Deripaska in a Ukrainian TV company called Black Sea Cable, according to legal filings by Deripaska's representatives.

In the filing, Deripaska accused Manafort and his associates of taking the money and then failing to respond to his queries about how the funds had been used.

Early in the 2016 presidential campaign, Deripaska's representatives openly accused Manafort of fraud and pledged to recover the money from him. After Trump earned the presidential nomination, Deripaska's representatives said they would no longer discuss the case.

Last week, Deripaska wrote in a statement to the AP that "there was an agreement between Mr. Deripaska and Mr. Manafort to provide investment consulting services related to business interests of Mr. Deripaska, which now is a subject to legal claims."