In the early hours of July 26, a team of FBI agents stormed former Trump campaign chairman Paul Manafort's home under orders from Special Counsel Robert Mueller, the Washington Post reports. The raid, along with Mueller's impaneling of a grand jury in DC last week, suggests that the investigator's Russia probe is growing increasingly aggressive.

According to the Post, agents used a search warrant to confiscate a number of documents and other records, though their specific contents are unclear. Manafort has already handed over materials to the Senate Judiciary Committee and the Senate and House intelligence committees, which are also investigating Russia's interference in the 2016 elections and any possible collusion between the Kremlin and Trump's campaign. Those documents reportedly pertain to a meeting Manafort took at the request of Donald Trump Jr. with a Russian lawyer who promised damaging information about Hillary Clinton last June.

Mueller is conducting his own, independent probe, which took on new vigor last week when he impaneled a Washington grand jury for the inquiry—allowing him to subpoena documents, secure sworn testimony, and indict suspects, the Wall Street Journal reports. According to the Post, the raid at Manafort's Virginia home suggests that Mueller's team might have reason to think he wouldn't produce all the records they planned to order him to turn over.

Manafort left his role as President Trump's campaign manager shortly after the New York Times released a bombshell report on his shady involvement with a pro-Russian political party in Ukraine. He's been accused of taking millions in undisclosed cash from the party and lobbying in Washington on its behalf—but failing to register in the US as a foreign agent. He ultimately did register in June, almost a year after leaving the Trump campaign.

Though Manafort has admitted he worked for the pro-Russian party, he's denied any wrongdoing and called accusations that he accepted off-the-books cash payments from the party "unfounded." His spokesman, Jason Maloni, claims the former campaign chairman was corporative during the predawn raid.

"FBI agents executed a search warrant at one of Mr. Manafort's residences," Maloni told Politico. "Mr. Manafort has consistently cooperated with law enforcement and other serious inquiries and did so on this occasion as well."