“My comments did not represent the actual timing or circumstances of any such discussions,” he added. “The point is that the proposal was in the earliest stage and did not advance beyond a free nonbinding letter of intent.”

Mr. Cohen pleaded guilty late last year to lying to Congress about the duration of the Moscow proposal; he had indicated initially that it stopped in January 2016.

It was not the first time Mr. Giuliani has reversed himself in his comments about issues related to the investigation of Russian election interference that is being led by the special counsel, Robert S. Mueller III.

Last week, Mr. Giuliani backtracked from another surprising assertion that left open the possibility that Trump campaign aides might have coordinated with Russia in its election interference in 2016.

“There was no collusion by President Trump in any way, shape or form,” Mr. Giuliani said in a statement on Thursday, reiterating the president’s longstanding defense against accusations that his campaign secretly coordinated with Moscow to help swing the election. “Likewise, I have no knowledge of any collusion by any of the thousands of people who worked on the campaign.”

He added, referring to discredited conspiracy theories that the president and his allies have long cited, “The only knowledge I have in this regard is the collusion of the Clinton campaign with Russia, which has so far been ignored.”

A day earlier, Mr. Giuliani stopped short of defending Trump campaign aides, drawing speculation that he might have inside knowledge of possible coordination with Russia.