Michael Flynn speaking at the US Institute of Peace "2017 Passing the Baton" conference in Washington on January 10. REUTERS/Yuri Gripas Former national security adviser Michael Flynn will invoke his Fifth Amendment rights and decline a subpoena issued by the Senate Intelligence Committee for documents related to his interactions with Russian officials from June 2015 to January 2017, the Associated Press reported Monday.

The documents were subpoenaed after Flynn's lawyer, Robert Kelner, declined to provide them by the original April 28 deadline.

Kelner did not respond to request for comment, but he wrote in a letter to the committee that a daily “escalating public frenzy against" Flynn and the Justice Department’s appointment of a special counsel have increased the chances that “any testimony he provides could be used against him," according to the AP.

Flynn asked for immunity from prosecution in late March in exchange for agreeing to testify before House and Senate committees about Russia's election interference.

The committees have yet to take him up on that offer, but if they did, then Flynn would be required to comply with their requests, said Andrew Wright, an associate professor at Savannah Law School who specializes in federal criminal law and national security.

Wright said Flynn's plan to invoke his Fifth Amendment rights against self-incrimination "will not play well publicly because many in Congress, the media, and the public will interpret it as an admission of guilt."

"However," Wright continued, "there are good reasons for Flynn's lawyer to recommend an assertion of privilege whether he is guilty of a crime or not."

But that is only when it comes to testifying, according to Todd Bussert, a federal criminal defense attorney in Connecticut.

Bussert told the Washington Post that while Flynn and his lawyers "may have valid Fifth Amendment claims — they couldn’t be compelled to speak to agents or what have you — they can’t refuse to comply with the subpoena for documents. You have to produce those — even though those may be incriminating.”

"It is Mike Flynn's right to plead the 5th," Republican Sen. James Lankford, a member of the Senate Intelligence Committee, tweeted on Monday. "We will get to the truth one way or another. We need facts, not speculation & anonymous sources."

The chairman and ranking member of the Senate Intelligence Committee, Sens. Richard Burr and Mark Warner, largely echoed Lankford's comment in a statement on Monday.

"While we recognize General Flynn’s constitutional right to invoke the Fifth Amendment, we are disappointed he has chosen to disregard the Committee’s subpoena request for documents relevant and necessary to our investigation," they wrote. "We will vigorously pursue General Flynn’s testimony and his production of any and all pertinent materials pursuant to the Committee’s authorities.”

U.S. President Donald Trump leaves the Central Intelligence Agency (CIA) headquarters accompanied by now-former National Security Adviser General Michael Flynn (2nd L) after delivering remarks during a visit in Langley, Virginia U.S., January 21, 2017. REUTERS/Carlos Barria

Trump, who has remained a fierce defender of Flynn since Flynn resigned on February 13, has in the past criticized requests for immunity and the invoking of one's Fifth Amendment rights.

"If you are not guilty of a crime, what do you need immunity for?" Trump said at a Florida campaign rally in September. Later that month, he slammed former staff members of Hillary Clinton who declined requests to testify about the former secretary of state's private email server.

"The mob takes the Fifth Amendment," Trump said at a rally in Iowa. "If you're innocent, why are you taking the Fifth Amendment?"

Flynn was forced to resign only 24 days after Trump appointed him national security adviser amid reports that he had discussed the issue of sanctions with Russia's ambassador to the US, Sergey Kislyak, before Trump's inauguration.

The House Oversight Committee announced earlier this month that Flynn had failed to disclose a $33,000 payment he received from Russia's state-owned news network in 2015 on security-clearance forms last year.

CNN on Friday reported that Russian officials boasted of their relationship with Flynn throughout 2016 and saw him as an ally who could help Moscow make inroads with Trump. At least two other former Trump associates, Paul Manafort and Carter Page, are under FBI investigation for their ties to Russia. A senior White House official is now caught up in the FBI's Russia investigation too, The Washington Post reported on Friday.

Page has so far declined to comply with the Senate Intelligence Committee's request for documents relating to his communications with Russians from June 2015 to January 2017. But he told Business Insider on Monday that he had not been subpoenaed and had "no intention to plead the Fifth, since I've never done anything wrong."