Talk show host David Letterman said Thursday he had testified before a grand jury earlier in the day about an extortion attempt. (John Paul Filo/CBS file/Associated Press)

Television talk show host David Letterman acknowledged on Thursday's show that he had sexual relationships with female employees and that someone tried to extort money from him over the affairs.

During the taping of his CBS late-night show in New York, Letterman discussed receiving a demand that he either pay $2 million or risk the relationships being made public.

In a release from the show's producer, Letterman said he referred the matter to the Manhattan district attorney's office and that an investigation ended in an arrest Thursday.

Letterman, 62, did not identify the person he said was arrested. But CBS said an employee has been charged with attempted grand larceny in connection with the case.

CBS said the employee worked on the show 48 Hours and has been suspended pending the results of the investigation. The network said the employee was arrested Thursday, hours before Letterman went public with his account during a taping of his show in New York.

U.S. media reports have named veteran CBS News producer Robert J. Halderman, 51, as the alleged suspect behind the plot.

As part of the investigation, Letterman said he issued a "phoney" $2 million cheque to the individual, and the arrest followed.

"This morning, I did something I've never done in my life," said Letterman. "I had to go downtown and testify before a grand jury."

In his testimony, he said he acknowledged sexual relationships with members of his staff.

"My response to that is, yes I have," Letterman said. "Would it be embarrassing if it were made public? Perhaps it would. I feel like I need to protect these people. I need to certainly protect my family."

CBS spokesman Chris Ender said Thursday that "Letterman's comments on the broadcast tonight speak for themselves."

Letterman and longtime girlfriend Regina Lasko married in March.

The couple began dating in 1986 and have a son, Harry, born in November 2003.