Jay Sekulow, a member of President Trump's legal team, said Sunday that "the president is not and has not been under investigation."

Sekulow's comments, in an interview with "Face the Nation," came after Mr. Trump slammed reports that FBI Special Counsel Robert Mueller is reviewing whether or not Mr. Trump tried to obstruct justice amid ongoing investigations into any ties between his presidential campaign's or transition's associates and the Russian government. The Washington Post first reported the story.

"They made up a phony collusion with the Russians story, found zero proof, so now they go for obstruction of justice on the phony story. Nice," Mr. Trump tweeted on Thursday.

They made up a phony collusion with the Russians story, found zero proof, so now they go for obstruction of justice on the phony story. Nice — Donald J. Trump (@realDonaldTrump) June 15, 2017

A day later, Mr. Trump said in a tweet, "I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt." He appeared to be referring to Deputy Attorney General Rod Rosenstein.

I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt — Donald J. Trump (@realDonaldTrump) June 16, 2017

But Sekulow says the legal team has "received no notice of investigation."

"There has been no notification from the special counsel's office that the president is under investigation," Sekulow said. "In fact, to the contrary. What we know is what James Comey said, the last thing we know is when he testified just a couple weeks back. That the President was not and is not a target of investigation."

He added, "I can't imagine a scenario where the president would not be aware of it. Number one, there is a serious constitutional issue here."

Sekulow, who is chief counsel at the American Center for Law and Justice, said that if the Post's reporting were accurate, Mr. Trump "would be under investigation for taking the action that the Department of Justice asked him to take. That raises not only a serious -- not even a serious constitutional question, it's an easy constitutional question. That's impossible. The president can not be investigated, or certainly can not be found liable for engaging in an activity he clearly has power to do under the constitution."

When asked if Mr. Trump interfered in the FBI's investigation, Sekulow said that in prior interviews, Mr. Trump "acknowledged that by firing James Comey as FBI director the president acknowledged that he would in fact probably extend the nature and length of the scope of the FBI, the special counsel probe."

Mr. Trump told reporters in a Rose Garden ceremony he would be "100 percent" willing to testify under oath, and Sekulow told CBS News' John Dickerson that "the president was very clear" about testifying and has said "if he was asked to do it he would."

Sekulow added that he thinks Mr. Trump will address the issue of any alleged tape recordings of Mr. Trump's conversation with Comey "in the week ahead," saying the tapes were not "priority number one" amid Mr. Trump's announcement to roll back President Obama's Cuba policies and Wednesday's shooting in Alexandria, Virginia.

"The president has a lot of issues and I think it shows that the president is concentrating on governing. This issue will be addressed in due course and I suspect next week."

The Secret Service has said it has no records of any recording systems or transcripts of any conversations Mr. Trump may have had in the White House.

The response comes after the Wall Street Journal reported on a May 15 Freedom of Information Act (FOIA) request they submitted to the Secret Service.