The chief executive of Cambridge Analytica has confirmed that the UK data research firm contacted Julian Assange to ask WikiLeaks to share hacked emails related to Hillary Clinton at about the time it started working for the Trump campaign in summer 2016.

Speaking at a digital conference in Lisbon, Alexander Nix said he had read a newspaper report about WikiLeaks’ threat to publish a trove of hacked Democratic party emails, and said he asked his aides to approach Assange in early June 2016 to ask “if he might share that information with us”, according to remarks published by the Wall Street Journal.

Assange, WikiLeaks’s founder, has already acknowledged the approach by Cambridge Analytica and said WikiLeaks rejected the request. In Lisbon, Nix reportedly agreed that the overture had been rebuffed.

“We received a message back from them that he didn’t want to and wasn’t able to, and that was the end of the story,” Nix said at the Web Summit conference, according to the WSJ. He called the exchange “very benign”.

However, the contacts between Cambridge Analytica and WikiLeaks are of interest to investigators looking into possible collusion between the Trump campaign and the Kremlin. The documents published by WikiLeaks in the summer of 2016 were later determined by US intelligence agencies to have been stolen by hackers working for Russian intelligence.

According to the Journal, citing emails and unnamed sources, Cambridge Analytica had sent employees to the Trump digital campaign headquarters and was in the process of finalising a contract with the campaign in early June of last year, apparently around the time Nix said he made the approach to Assange. It is not suggested that Cambridge Analytica made the approach at the Trump campaign’s request. The Guardian has contacted Cambridge Analytica for comment.

Representative Adam Schiff, the ranking Democrat on the House intelligence committee looking into possible Trump-Moscow collusion has said the committee had a “deep interest” in the relationship between Cambridge Analytica and WikiLeaks.

In an interview at the Web Summit, Nix rejected any suggestion of collusion with Russia.

“We did not work with Russia in this election, and moreover we would never work with a third-party state actor in another country’s campaign,” he said.

Robert Mercer, a Trump mega-donor, and his daughter, Rebekah, are major investors in Cambridge Analytica and Steve Bannon was a vice-president of the company before joining the Trump campaign and becoming the president’s chief strategist in the White House.

Cambridge Analytica’s website promises to help clients gain advantage over political opponents with its data analysts of US voter behaviour. It claims to hold up to 5,000 pieces of data on more than 230 million voters, to build a “psychographic” profile of targeted voters.

The company was hired to become part of the digital campaign, which was overseen by Trump’s son-in-law, Jared Kushner, and was paid $5.9m, according to the Federal Election Commission.