Donald Trump's transition team on Sunday demanded that Special Counsel Robert Mueller return "tens of thousands" of emails that were sent and received on government accounts before the 45th president took office.

A "source close to Trump's transition told Axios on Sunday that the team plans to send a letter to Mueller this week demanding the return of emails that were reportedly obtained by the Special Counsel's Office.

In the letter, the transition officials plan to say they will promise to return the emails to Mueller after "privilege" documents are redacted, according to Axios.

In a letter to Congress on Sunday, attorneys for the president argued that some of the emails should have been shielded by attorney-client privilege and other privileges.

A spokesperson for Mueller's office defended the way the emails were obtained in a statement over the weekend.

"When we have obtained emails in the course of our ongoing criminal investigation, we have secured either the account owner’s consent or appropriate criminal process,” spokesperson Peter Carr said.