President Trump has told friends and advisers that special counsel Robert Mueller's investigation is wrapping up and Mueller will soon write a letter clearing the president of any wrongdoing, sources told CNN.

A senior White House official and other sources close to the president said that Trump's legal team has told him that Mueller will exonerate him in the coming months, according to the network.

Trump also has reportedly been "less frustrated" in recent weeks with the investigation into whether his campaign colluded with Russia to win the election, marking a change.

He has repeatedly insisted in the past that there has been "no collusion" between his campaign and Moscow, and has referred to Mueller's investigation as a "witch hunt."

Trump allies, however, said the president may not be taking the investigation seriously enough, according to CNN.

Republican opposition to the investigation has intensified in the past week after it was reported that a member of Mueller's team had sent anti-Trump texts during the campaign. Calls of "political bias" in the FBI raised concerns that Trump would move to fire Mueller. The president reassured reporters over the weekend that he had no plans to do so.

Trump's lawyers are scheduled to meet with Mueller later this week, but Mueller has reportedly concluded all planned interviews with White House staff.