U.S. Commerce Secretary Wilbur Ross maintains investments in shipping company Navigator Holdings, leaked documents say. (Thew/Epa-Efe/Rex/Shutterstock/Thew/Epa-Efe/Rex/Shutterstock)

A trove of leaked documents known as the Paradise Papers created more Russia-related problems for the Trump administration Sunday, showing that Commerce Secretary Wilbur Ross holds business investments in companies tied to Russian President Vladimir Putin's inner circle.

The documents leaked as the administration faces several investigations into possible collusion between the Trump campaign and Russia, including a probe by special counsel Robert S. Mueller III that brought its first indictments last week. The millions of documents were attributed to the Bermuda-based Appleby law firm and were first leaked to the German newspaper Suddeutsche Zeitung.

They also were shared with the International Consortium of Investigative Journalists and its media partners around the world, including the New York Times and the Guardian. The Washington Post is not a member of the consortium and has not reviewed the materials.

The reports said Ross has maintained a financial interest through offshore investments in a shipping company called Navigator Holdings. One of the firm's largest clients is the Russian energy firm Sibur, a huge gas processing and petrochemicals company.

Among the firm's major stakeholders are Putin associate Gennady Timchenko, who individually is under U.S. sanctions, and Leonid Mikhelson, whom Forbes magazine lists as Russia's richest man and whose company, Novatek, is under sanctions. Another shareholder in Sibur is Kirill Shamalov, who is married to Putin's daughter. Neither Sibur nor Putin's son-in-law are sanctioned.

The full depth of Ross's financial holdings was not publicly clear during his confirmation process. Ross's investments in Navigator Holdings are in a string of companies located in the Cayman Islands. Ross disclosed his holdings in some of the companies when he became commerce secretary, but he was not required under the disclosure rules to declare his interest in Navigator.

Separately, the leaked documents showed that a Russian billionaire who has invested in a company co-owned by Jared Kushner, President Trump's son-in-law and White House adviser, bought a sizable number of shares in Twitter and Facebook. The social media companies have come under scrutiny for the way Russia is believed to have used them to try to influence last year's U.S. presidential election. Funding for the Facebook and Twitter stakes was provided through a state-controlled Russian bank and the financial arm of the state oil and gas company, according to the documents.

A spokesman for Ross told reporters Sunday that the commerce secretary recuses himself from matters involving trans­oceanic shipping and consults with ethics officials to make sure he is complying with the rules. The spokesman said Ross never met any of the three prominent Russians with stakes in Navigator Holdings.

The shipping company is publicly traded on the New York Stock Exchange. Ross's investment was approved by the Office of Government Ethics and apparently was never delved into by the Senate during his confirmation hearing.

Many Russian individuals and companies have been subjected to sanctions as a result of Russia's annexation of Crimea in 2014 and, more recently, over its suspected meddling in the U.S. election.

The Paradise Papers disclosures came as several investigations continue into whether there was any collusion between Russia and the Trump campaign in an effort to sway the election from Democrat Hillary Clinton. Mueller and committees in Congress are looking into Russia's activities. Trump has repeatedly denied collusion and dismissed reports about the investigations as "fake news."

But the latest document leaks raise more questions about business ties between Russia and some of the most prominent members of Trump's Cabinet. The New York Times reported that the documents include references to offshore holdings by Gary Cohn, the chief economic adviser, and Secretary of State Rex Tillerson. There is, however, no evidence that any of the holdings were illegal.

The documents reportedly show that Ross's investment firm, WL Ross, began buying shares of Navigator in 2011. He was given two seats on the company's board in return, although he resigned from the board in 2014.

When Ross became commerce secretary, he said he would retain his holdings in a few investment vehicles, including two with stakes in Navigator. A letter he wrote to the Commerce Department and the Office of Government Ethics said that some of the holdings he was keeping were involved in shipping, but he did not specify whether that included Navigator-related investments.

Another potentially damaging report concerned documents showing significant investments in Twitter and Facebook by Yuri Milner, a billionaire Russian technology magnate. The accounts said documents show that funding for Milner's purchases came from Russia's VTB Bank and the state-controlled Gazprom oil and gas company. Both companies are under U.S. sanctions.

According to the reports, VTB provided $191 million in 2011 for Milner to purchase a stake in Twitter. And Gazprom gave financing for an offshore company that provided money for $1 billion in Facebook stock. Milner, who is based in California, holds shares in dozens of Web companies, including Airbnb and Alibaba.

Milner also invested in 2015 in a start-up company in New York co-owned by Kushner and his brother. The start-up, Cadre, is an investment platform described as Uber for real estate. The investment was publicly announced at the time.

When Kushner became a White House adviser to his father-in-law, he did not disclose his ownership in Cadre on his initial financial disclosure form. He did disclose his ownership in BFPS Ventures LLC, which functions as a holding company and which held his ownership in Cadre.

In a statement he made in July to the Senate Intelligence Committee, Kushner said he never "relied on" Russian money to finance his private business dealings. Kushner declined to comment, through a spokesman, on the reports about Milner and his social media investments.

Milner has said his 2015 investment in Cadre amounted to $850,000. He also said VTB and Gazprom did not finance his shares in Facebook and Twitter.

Although there is no evidence the Russian investors used their funding to push political views, congressional investigations have raised questions about Russian-funded ads on Facebook and Twitter accounts that promulgated false and divisive narratives during the 2016 election.

David Filipov in Moscow and Amy Brittain contributed to this report.