A billionaire businessman who featured in the Paradise Papers exposé is under investigation by the US authorities on suspicion of bribing high ranking government officials in the Democratic Republic of the Congo, reports the UK Guardian.

A court ruling reveals for the first time that Dan Gertler, a close friend and adviser to the DRC president, is a key target of a US Department of Justice inquiry into alleged bribery in the mineral rich African republic.

The ruling, by judges in Switzerland, sums up the allegations made by US prosecutors against Gertler, who has made a fortune from diamond and mining businesses.

The US alleges he carried out transactions in DRC involving “the payment of bribes to high placed foreign public officials in exchange for securing and holding mining rights and government concessions and preferential treatment”.

The payments were allegedly made “both in cash and in kind, including in the form of luxury products and extravagant private travel”. The claim is that the bribes were received by three government officials.

The just published ruling is anonymised, and does not name Gertler, nor the company on behalf of which he was allegedly paying the bribes. The officials who are said to have received them are identified simply as “O, P and Q”.

However, a spokesperson for the Swiss justice ministry said the US had made three judicial assistance requests for evidence in relation to Gertler, and that the ruling related to these requests. Swiss judges have agreed to release documents to aid the US inquiry.

The partner for whose benefit Gertler is accused of paying bribes is described as a US hedge fund. The fund in question is believed to be Och-Ziff, which has already handed $213m (£150m) to the US authorities to settle criminal charges relating to the bribing of DRC officials. Och-Ziff declined to comment.

A spokesman for Gertler declined to comment. The businessman has previously stated that all allegations of illegal behaviour are “false and without any basis whatsoever”, that Gertler “rejects them absolutely”, and that he transacts business “fairly and honestly, and strictly according to the law”.

On Friday, Gertler’s lawyer Marc Bonnant confirmed to Swiss media that three demands for mutual legal assistance had been received from the United States, in connection with companies owned by his client.

Bonnant also confirmed that the UK’s Serious Fraud Office had sent requests for legal assistance to Switzerland regarding Gertler. He said these were in connection with a separate case.

It emerged in 2016 that the British were looking into mining concessions obtained in DRC from Gertler by a Kazakh company, Eurasian Natural Resources Corporation, which was listed in London at the time. A spokesperson for the SFO declined to comment.

The ruling reveals US prosecutors made a first request for mutual legal assistance from Switzerland regarding Gertler as long ago as 2012. This was followed by further formal requests in 2015 and 2016, and a demand for additional information in March 2017.

The requests were for the details of two Swiss bank accounts, in the name of separate companies. Prosecutors say some $26m may have been paid into the Zurich account of one of these companies.

Some of the banking data requested has already been handed over to the US, while more is pending as a result of supplementary requests, a spokesman for the Swiss justice ministry said. The US authorities declined to comment.

A close friend and adviser to DRC’s president, Joseph Kabila, Gertler has made a fortune from natural resources in Africa, much of which is controlled through offshore companies.

However, the businessman is under mounting pressure from law enforcement agencies. Gertler and 20 companies controlled by him were placed on the US sanctions list just before Christmas, and his assets have been frozen by the United States.

The move followed revelations from the Paradise Papers, a massive leak of documents from the offshore law firm Appleby. The files set out new information about Gertler’s dealings in DRC.