Conyers spoke in a rambling interview with WJBK host Mildred Gaddis, via telephone from an undisclosed hospital. Shortly afterwards his resignation letter was read on the floor of Congress.

Speaking to Gaddis, the 88-year-old insisted that the allegations against him did not diminish his half-century of service in Congress.

“My legacy can’t be compromised or diminished in any way by what we are going through now,” he said. “This too shall pass.”

Conyers went on to say of the allegations: “Whatever they are they are not accurate, they are not true and I think they are something that I can’t explain where they came from.”

He initially only spoke broadly about his political future, saying: “I am in the process of putting my retirement plans together will have more on that very soon.”

After prodding from Gaddis and a brief period of quiet, Conyers said: “Thank you for helping me get this into focus. I am retiring today and I want everyone to know how much I appreciate the support.”

Jerry Nadler of New York, the Democrat who recently replaced Conyers as the ranking member of the House judiciary committee, released a statement in which he said Conyers had been “a friend and mentor to me for over 25 years, and I am saddened that his service to our nation has had to end under these circumstances”.

The announcement came hours after Michigan state senator Ian Conyers, a grandson of John Conyers’ brother, told the New York Times the 88-year-old’s doctor “advised him that the rigor of another campaign would be too much for him, just in terms of his health”.

Conyers told the newspaper his great-uncle – the longest-serving current member of the House – was “not resigning”, adding: “He is going to retire.” The report did not specify how Ian Conyers knew of the congressman’s plans. He said he planned to run for John Conyers’ seat in Washington.

In the radio interview, Conyers endorsed his son John Conyers III to succeed him, not his great-nephew.

Conyers was first elected in 1964 and easily won re-election last year in the heavily Democratic 13th district. But following mounting allegations of sexual harassment, he has faced growing calls to resign from colleagues including the House minority leader, Nancy Pelosi.

He returned to Detroit from Washington last week and was hospitalized after complaining of feeling light-headed. His attorney, Arnold Reed, said Conyers’ health would be the paramount consideration in whether he decided to step down.

In his statement, Nadler said “there is no doubt that these allegations have taken a tremendous toll on [Conyers] personally, as well as on his family and on everyone that knows him.”

“With that said, there can be no tolerance for behavior that subjects women to the kind of conduct that has been alleged.”

A statement from Pelosi said: “Congressman Conyers … shaped some of the most consequential legislation of the last half-century. But no matter how great the legacy, it is no license to harass or discriminate.”

She added: “The brave women who came forward with were owed the justice of this announcement. Now, we must pass the ME TOO Congress Act to create greater transparency and accountability in the broken reporting and settlements system. We must lead the fight against sexual harassment and abuse, not only in Congress but in every workplace, everywhere in our country.”

The House ethics committee is reviewing allegations of harassment. On Monday, a woman who said she worked for Conyers for more than a decade said he slid his hand up her skirt and rubbed her thighs while she was sitting next to him in the front row of a church.

Elisa Grubbs made the allegation in an affidavit released by her attorney, Lisa Bloom. Grubbs is the cousin of another accuser, Marion Brown, who reached a confidential settlement with Conyers which she broke to speak publicly last week. Bloom posted Grubbs’ affidavit on Twitter and confirmed it was genuine. It says she worked for Conyers from approximately 2001 to about 2013.

She also said she saw Conyers touching and stroking the legs and buttocks of Brown and other female staffers on “multiple occasions”. Grubbs said witnessing such harassment “was a regular part of life while working in the office of Rep Conyers”.

Once when Grubbs was at Conyers’ home, she said, he came out of the bathroom naked when he knew she was in the room.

Reed told the Detroit Free Press the allegations by Grubbs were “another instance of tomfoolery from the mouth of Harvey Weinstein’s attorney”.

Bloom previously represented Hollywood executive Weinstein, who is accused of sexual misconduct and assault by a number of women. She quit Weinstein’s team after the allegations became public and now represents sexual harassment victims.