Special counsel Robert Mueller has asked Cambridge Analytica to turn over emails from employees who also worked for the Donald Trump presidential campaign.

The firm complied with the request and handed over documents both to Mueller and to the House Intelligence Committee, the Wall Street Journal reported.

Members of the Intelligence panel on Thursday interviewed the head of the data analysis firm to determine whether Trump's election campaign team sought his help to find thousands of emails missing from Hillary Clinton's private server, three sources familiar with the session said.

Trump's campaign hired Alexander Nix and Cambridge Analytica in June 2016 and paid it more than $6.2 million through last December, according to Federal Election Commission records.

Special counsel Robert Mueller has asked Cambridge Analytica to turn over emails from employees who also worked for the Donald Trump presidential campaign

The month after his firm was hired, Nix emailed WikiLeaks founder Julian Assange for help tracking down some 33,000 emails that Clinton supposedly had deleted from her private server, the Daily Beast and The Wall Street Journal reported in October.

A firm spokesman told the Journal Nix was 'very happy to volunteer his expertise and experience to help the committee with its important work, adding: “Cambridge Analytica remains committed to supporting and assisting the committee in any way that it can, including by honoring their direction not to discuss these matters publicly.'

At the White House Friday, President Trump got asked an open-ended question about whether Mueller was biased, and immediately offered a denial of any collusion with Russia.

'There is absolutely no collusion. That has been proven. When you look at the committees, whether it's the Senate or the House, everybody – my worst enemies, they walk out, they say, "There is no collusion but we'll continue to look." They're spending millions and millions of dollars,' the president said.

'There is absolutely no collusion. I didn’t make a phone call to Russia. I have nothing to do with Russia. Everybody knows it. That was a Democrat hoax. It was an excuse for losing the election, and it should have never been this way, where they spent all these millions of dollars.'

Trump continued: 'So now even the Democrats admit there's no collusion. There is no collusion -- that's it. And we got to get back to running a country.'

CEO of Cambridge Analytica, Alexander Nix, speaks during the Web Summit, Europe's biggest tech conference, in Lisbon, Portugal, November 9, 2017

Rebekah Mercer attends the 2017 TIME 100 Gala at Jazz at Lincoln Center on April 25, 2017 in New York City

Nix wanted to convert the missing and potentially damaging emails into a searchable database for use by the Trump campaign or a pro-Trump political action committee, the Journal reported.

WikiLeaks confirmed to Reuters on Thursday that it was approached by Nix, but a representative said it turned down his request.

Trump donor and Cambridge Analytica co-owner Rebekah Mercer reached out to Nix during the campaign and asked whether the firm could help organize Clinton emails being released by WikiLeaks to help make them more readily searchable.

It was on Mercer and her father Robert Mercer's recommendation that Trump brought on Steve Bannon as a top campaign advisor.

The intelligence committee is investigating possible collusion between Trump's campaign team and Russia during the 2016 election. The matter is also being investigated by Special Counsel Robert Mueller and three other congressional committees.

Russia has denied meddling in the election, and Trump has said there was no collusion between Moscow and his campaign.

Representatives Elijah Cummings and Jerrold Nadler, the top Democrats on the House Oversight and Judiciary committees, on Thursday asked their Republican committee chairmen to issue subpoenas for documents from Cambridge Analytica and Giles-Parscale, another data analysis firm that worked for the Trump campaign.

Spokesmen for Cambridge Analytica and Giles-Parscale did not immediately respond to emails requesting comment.

Cummings and Nadler said they sent their letter after the two companies declined to answer questions about whether they had contacts with foreign actors during the 2016 presidential campaign.

The sources said the intelligence committee members met at a Washington law office on Thursday to conduct the interview with Nix by Skype because he was not in the United States. The sources said the interview lasted some 90 minutes.

The CIA, Federal Bureau of Investigation and the National Security Agency said in January that Russia used propaganda, social media and other means to meddle in the 2016 election to try to help Trump defeat Clinton.

In their report, the agencies said Russian intelligence services hacked emails and other documents from the Democratic National Committee and other Democratic Party organizations, and used Wikileaks to release them. (Reporting by Jonathan Landay and Mark Hosenball; Editing by John Walcott, Kieran Murray, Toni Reinhold)