The home of Paul Manafort, President Donald Trumps former campaign chairman, was raided by FBI agents in July, The Washington Post reports .

A Manafort spokesman confirmed the raid to ABC News .

FBI agents executed a search warrant at one of Mr. Manaforts residences, he said in a statement. Mr. Manafort has consistently cooperated with law enforcement and other serious inquiries and did so on this occasion as well.

Manafort had no advance warning about the raid, which took place July 26. According to the Post, documents and other materials were seized.

Manafort is a key figure in the investigation into the Trump campaigns ties to Russia.

One day before the raid, Manafort met with Senate Intelligence Committee investigators to discuss a meeting of a Russian lawyer and members of Trumps campaign team that took place during the 2016 presidential election. Manafort spokesman Jason Maloni said the former campaign chairman answered their questions fully.

On June 27, Manafort retroactively registered as a foreign agent thanks to $17.1 million his firm was paid from 2012 to 2014 for lobbying work he did on behalf of a pro-Russian political party in Ukraine.

Manafort ran Trumps campaign in 2016 from March to August, when he resigned after questions were raised about that work.

Special counsel Robert Mueller has enlisted a grand jury in Washington, D.C., to advance his Russia investigation. Grand juries can be used as legal tools in cases where there is the possibility of criminal conduct , but their use doesnt necessarily signify criminal charges will be brought.

Trump has maintained that the Russia investigation is a witch hunt , despite several officials including Christopher Wray, his pick to replace James Comey as FBI director, and Sen. John Thune (R-S.D.) saying otherwise .

Trump commented on the raid Thursday afternoon, calling it a very, very strong signal, or whatever and saying he was very, very surprised to hear of the raid.

Ive always found Paul Manafort to be a very decent man. Hes like a lot of other people, probably makes consultant fees from all over the place, who knows, I dont know, but I thought it was pretty tough stuff to wake him up, perhaps his family was there, Trump told reporters at his golf club in Bedminster, New Jersey. I think thats pretty tough stuff.

This story has been updated with more background on Manafort and the investigation, as well as with Trumps comments from Thursday.

CORRECTION: An earlier version of this article said Manafort registered as a foreign agent on July 27. It was June 27.