WASHINGTON (Reuters) - Preliminary discussions are under way for Special Counsel Robert Mueller to potentially interview U.S. President Donald Trump as part of the probe of alleged Russian interference in the 2016 election, NBC News reported on Monday.

Citing three people familiar with the situation, NBC said lawyers for Trump had met with representatives of Mueller’s office in late December to talk about the logistics of any such interview.

The discussions included the possible location and length of any interview as well as legal standards and options for its format, including written responses instead of a formal sit-down, according to the news network.

Mueller, under the Department of Justice, is investigating allegations of Russian meddling in the U.S. presidential election and possible collusion by Trump’s campaign.

U.S. intelligence agencies have concluded that Russia interfered in the election to try to help Trump win. Russia has denied any meddling, and Trump has said there was no collusion.

Democratic U.S. Senator Richard Blumenthal told MSNBC News on Monday that he expected Mueller would try to talk to the president in person.

“He will interview the president face-to-face is my prediction,” said Blumenthal, a member of the Senate Judiciary Committee, which is conducting its own Russia investigation.

Mueller’s probe so far has led to two Trump associates, former National Security Adviser Michael Flynn and campaign aide George Papadopoulos, pleading guilty to lying to FBI agents in the investigation.

Two others, Trump’s former campaign manager Paul Manafort and his associate Richard Gates, have also been indicted but have pleaded not guilty. Manafort sued Mueller’s office last week, saying the special counsel’s investigation exceeds its legal authority.

Lawyers for the president, including Ty Cobb, John Dowd and Jay Sekulow, did not immediately reply to requests for comment or were unavailable.

The spokesman for the special counsel’s office, Peter Carr, did not immediately respond to a request for comment.

Trump has repeatedly said he personally is not under investigation.

Asked on Saturday if he would speak with Mueller’s team, Trump said he would. He also defended his legal team’s work.

”There’s been no collusion; there’s been no crime,“ he told reporters while at the Camp David presidential retreat in Maryland. ”And in theory, everybody tells me I‘m not under investigation.

“We have been very open,” Trump said. “ ... We could have been very closed, and it would have taken years. But you know, it’s sort of like, when you’ve done nothing wrong, let’s be open and get it over with.”