Political strategist Roger Stone, a long-time ally of President Trump, has been arrested in Florida, charged with seven counts in the Mueller probe.
Mr Stone will appear in court later in the city of Fort Lauderdale.
The indictment includes one count of obstruction of an official proceeding, five counts of false statements, and one count of witness-tampering.
The charges are linked to an alleged Russian-led hack into the emails of Democratic Party officials.
The information contained in the emails was released by WikiLeaks during the 2016 US presidential election campaign.
CNN reports that FBI agents arrested Mr Stone in a pre-dawn raid on Friday. One pounded on the door and said, “FBI… Open the door,” the US outlet says.
What links Stone to the email hack?
Hillary Clinton’s 2016 campaign chairman John Podesta, who was targeted in the email hack, accused Mr Stone of knowing about it beforehand.
According to investigators, Mr Stone said he had “communicated” with WikiLeaks founder Julian Assange before the emails’ release and had described the contact as “perfectly legal”.
The indictment accuses the lobbyist of lying to the House Intelligence Committee about what passed between him and WikiLeaks, and of falsely claiming not to have records of it.
Mr Stone is said to have spoken to senior Trump campaign officials – who are not identified – about “organization 1” [believed to be WikiLeaks] “and information it might have had that would be damaging to the Clinton Campaign”.
Prosecutors say Mr Stone was also “contacted by senior Trump campaign officials to inquire about future releases” by WikiLeaks.
His campaign activities have long been under scrutiny by Special Counsel Robert Mueller, who is investigating allegations of collusion between Russia and the Trump campaign.
In 2016, US intelligence agencies concluded that Russia had tried to turn the election in Mr Trump’s favour through a state-authorised relay of cyber attacks and fake news stories planted on social media.
Mr Trump has branded the Mueller inquiry a political “witch-hunt”. The Kremlin has always denied meddling in the US election.
Mr Stone has repeatedly said in interviews that he expected to be indicted. In May he told NBC’s Meet The Press: “It is not inconceivable now that Mr Mueller and his team may seek to conjure up some extraneous crime pertaining to my business, or maybe not even pertaining to the 2016 election.
“I would chalk this up to an effort to silence me.”
Who’s been charged in the Mueller probe?
Mr Stone is the 34th person to be charged as part of the Mueller investigation. Those indicted include 12 Russian military officers and 13 Russian nationals accused of leading a campaign to interfere in the US election.
Another three Russian entities, including the notorious Internet Research Agency “troll farm”, have also been charged.
Several people connected directly with Mr Trump have been indicted, including his former national security adviser Michael Flynn, and Paul Manafort, the former chairman of his election campaign, who is in jail.
Who is Roger Stone?
A long-time friend of Donald Trump, Roger Stone has worked on Republican political campaigns since the 1970s.
The 66-year-old favours three-piece suits and reportedly refuses to wear socks.
He began his career working on Richard Nixon’s 1972 re-election bid, and has a tattoo of the 37th president across his shoulder blades.
Mr Stone published a book, The Making of the President 2016, after helping Mr Trump to power.