Fox News has learned that federal investigators kept a register of phone calls made by President Trump's personal attorney, Michael Cohen, but those calls were not recorded, contrary to an earlier report by NBC News.

Sources with knowledge of the proceedings told Fox News that investigators used a pen register, or dialed number recorder (DNR), on at least one of Cohen's phones. A pen register records all numbers dialed from a given phone number, as well as the length of each call.

The National Security Agency (NSA) gathers similar information, which is sometimes referred to as metadata.

Further, in an April 13 court filing, prosecutors revealed they had, "already obtained search warrants ... covert until this point ... on multiple different email accounts maintained by Cohen."

"We already have considerable amounts of information about Mr. Cohen’s activities," Assistant U.S. Attorney Thomas McKay said during the hearing in reference to warrants obtained in the course of the investigation.

Earlier Thursday, NBC reported that Cohen's conversations had been recorded in the weeks leading up to FBI raids on his home, office and hotel room last month. The report also claimed that investigators recorded at least one call made to the White House from a number associated with Cohen.

NBC later added an editor's note to the online version of its report saying that "three senior U.S. officials" had disputed the original wiretap report.

At Thursday’s briefing, White House Press Secretary Sarah Sanders referred questions about the report to Trump’s outside counsel. “I can’t verify the validity of that report,” she said.

The FBI and U.S. attorney’s office had no comment when reached by Fox News.

A spokesperson for the Trump Organization, where Cohen used to work, said in a statement: “Mr. Cohen has not worked for the company for more than a year. In any event, we have no knowledge of any nonpublic investigative actions with respect to Mr. Cohen.”

The erroneous NBC report added to widespread speculation about what exactly the feds were able to seize in their April raid. Cohen’s lawyers and Trump’s team have been battling in court over access to those materials.

NBC also reported that New York city's onetime mayor, Rudy Giuliani, who recently joined Trump’s legal team, learned that Trump had made a post-raid call to Cohen. Giuliani reportedly told Trump not to call again out of concern that the conversation could be recorded.

Cohen is being investigated in a grand jury probe of his personal and business dealings, which include a $130,000 payment made to adult film star Stormy Daniels in exchange for her silence about an alleged sexual encounter with Trump in 2006.

The U.S. Attorney’s Office for the Southern District of New York says that Cohen has been under investigation for months, and that it was behind the raid.

Giuliani, meanwhile, revealed on Fox News' "Hannity" on Wednesday night that Trump reimbursed Cohen for that payment – despite Trump’s past comments denying knowledge of it – but said the president thought it was just for unspecified "expenses" at the time.

Giuliani also has blasted the separate probe of alleged Russian meddling in the 2016 elections by a special counsel, calling Thursday for it to be shut down.

Fox News’ Brooke Singman and Adam Shaw contributed to this report.