Special counsel probing flow of Russian-American money to Trump political funds Contributions from Americans with Russia ties is of interest to investigators.

 -- Three Americans with significant Russian business connections contributed almost $2 million to political funds controlled by Donald Trump, ABC News has learned.

The timing of contributions coming from US citizens with ties to Russia is now being questioned by investigators for special counsel Robert Mueller, according to a Republican campaign aide interviewed by Mueller’s team.

Unless the contributions were directed by a foreigner, they would be legal, but could still be of interest to investigators examining allegations of Russian influence in the 2016 campaign, said Rep. Adam Schiff of California, the ranking Democrat on the House Intelligence Committee.

“Obviously, if there were those that had associations with the Kremlin that were contributing, that would be of keen concern,” Schiff told ABC News.

A review of Trump campaign records conducted by the Center for Responsive Politics for ABC News found large contributions coming from two émigrés born in the former Soviet Union who now hold U.S. citizenship, and from a third American who heads the subsidiary of a large Russian private equity firm.

Those donations began flowing to the Republican National Committee, the group says, just as Trump was on the verge of securing the Republican nomination and culminated in two large gifts – totaling $1.25 million – from these individuals to the Trump inaugural fund following his victory.

Government officials familiar with the House and Senate investigations into Russian election interference told ABC News that near the conclusion of the June 2016 Trump Tower meeting involving Trump’s son Don Jr., son-in-law Jared Kushner, then-campaign chairman Paul Manafort, and Russian emissaries interested in curtailing U.S. sanctions, Manafort made a cryptic and cursory notation on his phone. It said, “Active sponsors of RNC,” a phrase that some investigators have viewed as a reference to campaign donations, the sources said.

Manafort spokesman Jason Maloni disputed any notion that he was referencing contributions, telling ABC News any assertion that they talked money was “not true.”

“This sounds like more Washington whispers,” Maloni said. “Anonymous sources with self-serving motives peddling rumors and speculation.”

Sheila Krumholz, executive director of the Center for Responsive Politics, which specializes in analyzing and tracking political contributions, said she would expect the special counsel to look closely at one of the most time-honored ways to exert influence in an election -- donations.

“I think it will be a dereliction of duty for the investigators and special counsel Mueller not to look into” that flow of money, Krumholz said.

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Leonard Blavatnik, a Ukrainian-born billionaire who holds American and British citizenship, has contributed $383,000 to the Republican National Committee since late April 2016 and added another $1 million to Trump’s inauguration fund. Those figures include more than $12,000 that was later directed into President Trump’s legal defense fund, as first reported by the Wall Street Journal. He did not give directly to the Trump campaign.

Blavatnik made his fortune in heavy industry and oil and gas after the fall of the Soviet Union, expanding his Russian holdings under Putin through a lucrative oil deal while also purchasing familiar Western brands such as the Warner Music Group, which he bought in 2011 for $3.3 billion.

He has donated tens of millions of dollars to educational and charitable causes and prefers to be known as an American philanthropist. He also has a long history of political giving to PACs supporting candidates of both parties. He gave $1.5 million for Sen. Marco Rubio during the early 2016 primary campaign, as well as $1 million for Wisconsin Gov. Scott Walker and $800,000 for South Carolina Sen. Lindsey Graham. In 2011, he gave for both President Barack Obama and his GOP challenger, former Massachusetts governor Mitt Romney.

When asked if Blavatnik had been contacted by federal investigators about his contributions during and after the 2016 campaign, a spokesperson told ABC News the billionaire would not comment. In an earlier statement made to British media, Blavatnik noted that neither his contributions, nor those of his company Access Industries, were made directly to Trump.

"Access Industries made a donation to the Presidential Inaugural Committee, a joint Congressional committee that has been responsible for organizing the inauguration ceremonies of every U.S. president since 1901 and which helps to organize public and private events during the week leading up to the Inauguration,” the statement said. "The types of events that the Presidential Inaugural Committee plans and supports include public concerts, fireworks, lunches, dinners, the inauguration ceremony, and the inaugural parade.”

Krumholz, however, said the donations to the inauguration are hard to view as having a solely charitable motive. Blavatnik, she said, is a political “heavy hitter,” and longstanding political donor. “He runs Access Industries and I think the name probably says it all,” she said.

Additional contributions from Russian-connected donors came from Russian-born oil executive Simon Kukes and New York businessman Andrew Intrater, who oversees the U.S. arm of the Russian conglomerate Renova Group. Neither Kukes nor Intrater had an appreciable record of political contributions until last year, according to the Center for Responsive Politics.

After Trump secured the nomination, Kukes gave $280,000 to an assortment of Trump-controlled funds over the next several months. Intrater contributed $35,000 to the Trump Victory committee, plus $250,000 to Trump’s inauguration fund.

Neither Kukes nor Intrater returned messages left at their homes and offices.

All three men -- Blavatnik, Kukes, and Intrater -- have been publicly identified as associated with Viktor Vekselberg, considered one of the richest men in Russia. Vekselberg is reported to hold frequent meetings with President Vladimir Putin as part of a business group known as the Russian Union of Industrialists and Entrepreneurs. Emails to Vekselberg’s Moscow-based company, Renova, were not returned. Vekselberg’s firm, the Renova Group, has also donated between $50,000 and $100,000 to the Clinton Foundation.

Experts who follow the activities of Russia’s cadre of billionaires, commonly known as the “oligarchs,” told ABC News they believe donations from these three men, all of whom have worked closely with Vekselberg, warrant intense scrutiny.

Louise Shelley, director of the Terrorism, Transnational Crime and Corruption Center at George Mason University, said she does not believe large contributions from Blavatnik or from donors associated with Vekselberg would occur without the implicit approval of the Kremlin.

“If you have investments in Russia then you cannot be sure that they are secure if you go against the Kremlin's will,” Shelley said. “You can't be an enormously rich person in Russia, or even hold large holdings in Russia without being in Putin's clutches.”

Both Blavatnik and Vekselberg had crossed paths with officials in Trump’s inner circle prior to the real estate mogul’s run for president.

After Trump supporter and now Commerce Secretary Wilbur Ross took a controlling interest in the Bank of Cyprus, for instance, a company controlled by Vekselberg became the biggest single Bank of Cyprus shareholder. During Ross’s confirmation hearings in February, a group of six Democratic senators raised questions about the nominee’s ties to Vekselberg. They noted that Vekselberg had served on the board of the Russian oil company, Rosneft, which was placed under sanctions in 2014 after Russia’s armed incursion into Crimea.

Vekselberg also oversaw fundraising for the Moscow Jewish Museum, including hosting a 2014 gala in Russia attended by Trump’s daughter Ivanka and her husband, Jared Kushner. Blavatnik also attended the event.

In addition, both men have business ties to another Russian oligarch, Oleg Deripaska, whose name has already surfaced in connection with the Mueller investigation -- Deripaska was a client of Manafort’s prior to joining Trump’s campaign, as first revealed in Manafort’s foreign registration filings. Deripaska is the majority owner of RUSAL, the world's second largest aluminum company. Vekselberg and Blavatnik hold a significant interest in RUSAL, and Blavatnik served on the company’s board until shortly after Trump was elected.

Ilya Zaslavskiy, an Oxford-trained scholar and frequent critic of the oligarchs, told ABC News there is good reason for concerns about the role Vekselberg and Blavatnik may have played in the 2016 elections, given what he says was “a continuous relationship of these oligarchs with Kremlin and security services.”

Special counsel Mueller “should absolutely look into this because these people have a track record of very close relationships with the Kremlin,” Zaslavskiy said. “There is now overwhelming evidence that Putin has run a multilayered, sophisticated campaign against American institutes.”

Schiff said he has not reached any firm conclusions, but his committee will be looking closely at every facet of the Russian influence effort, including political donations from billionaires with lasting ties inside Russia.

“The oligarchs are really part and parcel of service to the Kremlin,” Schiff said. “They can be called upon at basically Putin’s will to do what he needs done. It gives them some distance from the Kremlin, it gives them some plausible deniability.”

Shelley said the country may never know if the contributions were made independently or covertly directed by the Kremlin. But she believes that in the 2016 presidential contest, anyone with deep business investments in Russia “would not be contributing to Hillary, [and] Russians would not be aligning themselves with Hillary, because they knew that Putin really disliked her.”

ABC News' James Gordon Meek, Alex Hosenball and Cho Park contributed to this report.