Bernie Sanders has warned that the world is rapidly becoming an “international oligarchy” controlled by a tiny number of billionaires, highlighted by the revelations in the Paradise Papers.

In a statement to the Guardian in the wake of the massive leak of documents exposing the secrets of offshore investors, Sanders said that the enrichment of wealthy individuals and companies in tax havens was “the major issue of our time”.

He said the Paradise Papers opened the door on a “major problem not just for the US but for governments throughout the world”.

“The major issue of our time is the rapid movement toward international oligarchy in which a handful of billionaires own and control a significant part of the global economy. The Paradise Papers shows how these billionaires and multinational corporations get richer by hiding their wealth and profits and avoid paying their fair share of taxes,” the US senator from Vermont said.

Sanders, who came in a close second to Hillary Clinton in the race for the Democratic presidential nomination last year, pointed the finger of blame for the flourishing of offshore holdings on both Congress and the Trump administration. He told the Guardian that Republicans in Congress were responsible for providing “even more tax breaks to profitable corporations like Apple and Nike”.

The same tax breaks, he said, were being seized upon by super-wealthy members of Trump’s cabinet “who avoid billions in US taxes by shifting American jobs and profits to offshore tax havens. We need to close these loopholes and demand a fair and progressive tax system.”

Sanders’ intervention in the debate sparked by the Paradise Papers marks the most prominent political response to the leak in their opening 24 hours. The investigation stems from the leak of some 13m files obtained by SÃ¼ddeutsche Zeitung in Germany and shared with almost 100 news organisations around the world including the Guardian by the International Consortium of Investigative Journalists.

One of the most pointed disclosures in the Paradise Papers was that Wilbur Ross, Trump’s commerce secretary, has continued to do business with the son-in-law of the Russian president, Vladimir Putin, as well as a member of Putin’s inner circle who is under US sanctions. Ross, himself a billionaire, has retained since joining the Trump administration his investment in a shipping company, Navigator, that has a partnership with the Russian gas giant Sibur.

In turn Sibur is part-owned by Kirill Shamalov, the husband of Putin’s daughter.

The emergence of Ross’s ongoing ties to business interests so close to the Russian president at a time of intense scrutiny of the relationship between the Trump administration and the Kremlin has incensed prominent Democrats involved in Ross’s confirmation to office. Richard Blumenthal, a Democrat who sits on the US Senate commerce committee, accused Ross of deceiving the public as well as lawmakers who had allowed the confirmation to go through having heard Ross promise to divest himself of any interests that carried potential conflict.

“If he fails to present a clear and compelling explanation, he ought to resign,” Blumenthal told MSNBC in an interview.

Senator Tammy Baldwin, a Democrat from Wisconsin, said: “In February, I opposed Mr. Ross’ nomination because there were a number of unanswered questions about his ownership stake in the Bank of Cyprus and his connections to Russian President Vladimir Putin, as well as his refusal to divest from a $1 billion co-investment made with the state-owned Chinese Investment Corporation.

“Despite assurances from the Commerce Department and the White House on the eve of his nomination, these questions remain unanswered over eight months later. These unanswered questions and recent revelations certainly warrant a Commerce Committee hearing and I think an Inspector General investigation is in order. We should get to the bottom of this.”

On Monday, Ross denied that he had done anything wrong in his handling of his investment in Navigator. In the course of a visit to London, he told UK media that “there is nothing wrong with it. The fact that it happens to be called a Russian company doesn’t mean there is any evil in it.”

Further responses to the Paradise Papers came from the Democratic leader in the US Senate Chuck Schumer, and the ranking Democratic member of the Senate finance committee, Ron Wyden. In a joint statement they accused Republicans in Congress leading the push towards a reform of the tax code of failing to close egregious loopholes revealed by the leaks.

As a result Republicans were rewarding, the duo said, “wealthy billionaires like secretary Wilbur Ross for dodging taxes, while punishing many in the middle class with new tax hikes. If you deduct medical expenses or student loan interest from your taxable income, the Republican plan comes after your wallet. But if you stash your billions in secret bank accounts overseas, their plan gives you the green light to keep doing what you’ve been doing.”

They added that the Paradise Papers were “proof positive that the Republican tax plan favours the wealthy and betrays the middle class in this country, who are the ones left carrying the financial burden of massive corporate tax avoidance”.