Former White House chief of staff Reince Priebus has submitted to questioning by investigators looking into Russian interference in the United States presidential campaign.
Mueller is now reportedly looking into the circumstances surrounding President Trump's firing of James Comey as Federal Bureau of Investigation director in May.
United States media are reporting the Mr Priebus was questioned in the probe into possible collusion by associates of President Donald Trump.
Furthermore, she said, "what has to worry the White House right now" is that Priebus - former director of the Republican National Committee - is not a family relation to the president like Jared Kushner or Donald Trump, Jr nor is he a "true believer" like Steve Bannon.
He spoke with special counsel Robert Mueller's team "voluntarily" about its probe into Russia's alleged involvement in the USA presidential election.
Reince Priebus, President Trump's former White House chief of staff, was interviewed by Special Counsel Robert Mueller's team Friday as part of the probe into Russia's alleged attempt to meddle in the 2016 election, his lawyer said. "He was happy to answer all of their questions".
William Burck said Priebus' interview took place at Mueller's office. His voicemail box was full.
White House lawyer Ty Cobb is clearing through a backlog of requests from Mueller for documents and information from the Trump administration, according to two people familiar with the investigation. Among the other officials his team is expected to interview are former press secretary Sean Spicer and White House counsel Don McGahn.