President Trump on Thursday ripped into Special Counsel Robert Mueller’s Russia investigation, accusing investigators of having “gone absolutely nuts” and saying they are “a disgrace” to the country.

“The inner workings of the Mueller investigation are a total mess. They have found no collusion and have gone absolutely nuts,” Trump tweeted. “They are screaming and shouting at people, horribly threatening them to come up with the answers they want. They are a disgrace to our Nation and don’t care how many lives the[y] ruin.”

He then focused his ire on Mueller, a former FBI director, who he accused of having conflicts of interest, though he did not elaborate on the accusation. Mueller served under both George W. Bush and Barack Obama.

“These are Angry People, including the highly conflicted Bob Mueller, who worked for Obama for 8 years. They won’t even look at all of the bad acts and crimes on the other side,” he said. “A TOTAL WITCH HUNT LIKE NO OTHER IN AMERICAN HISTORY!”

He later went on to say that universities would study what Mueller "and his gang of Democrat thugs have done to destroy people."

The barrage comes as Trump’s legal team is believed to be finalizing written answers to Mueller, concerning questions about whether the Trump campaign colluded during the 2016 campaign.

TRUMP TEAM FINALIZING ANSWERS TO MUELLER PROBE QUESTIONS, SOURCES SAY

The president has repeatedly denied any claims of collusion, and has dismissed the probe as a witch hunt. On Thursday, he tweeted that "the only 'collusion' is that of the Democrats with Russia and many others," before asking why the FBI didn't confiscate Hillary Clinton's private email server and accusing social media companies of being biased in favor of Democrats.

Late last month, Trump lawyer Rudy Giuliani told Bloomberg News that a face-to-face interview was "off the table," though he did not definitively rule out the possibility.

The Associated Press reported this week that Trump advisers are concerned that Mueller has been stealthily compiling information and could soon issue new indictments (it has so far produced 32 criminal charges) or a highly critical final report.

Attorney General Jeff Sessions, who recused himself from the Russia probe last year, was forced to resign last week by Trump, and replaced by Acting Attorney General Matthew Whitaker. Whitaker has been facing calls to recuse himself from the Russia probe due to his criticism of the investigation.

Fox News’ Samuel Chamberlain, Catherine Herridge and The Associated Press contributed to this report.