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.
Special Counsel Robert Mueller is investigating alleged collusion between Russia and the Trump campaign.
President Trump denies he or his campaign staff worked with Russia to boost his candidacy in the 2016 US presidential election, and has called the Mueller inquiry "a witch-hunt".
So far Mr Mueller's investigation has led to charges against more than two dozen Russians, as well as several people connected to Mr Trump himself, including his former national security adviser Michael Flynn, and Paul Manafort, the former chairman of his election campaign.
Mr Stone was detained in a pre-dawn arrest.