The New York City Ballet and its affiliated training arm, the School of American Ballet, are investigating allegations of sexual harassment against Peter Martins, who heads both institutions, according to statements issued Monday night. Martins, 71, has been removed from teaching his weekly class at SAB while the investigation is underway.

The allegations were made in an anonymous letter, which made “general, non-specific allegations of sexual harassment in the past by Peter Martins at both New York City Ballet and the School,” SAB said in its statement. SAB said it had hired a law firm to conduct “a thorough investigation.”

“Thus far, the investigation has not substantiated the allegations in the letter or discovered any reason to be concerned about student safety,” the statement said.

NYCB issued a similar statement that said  the letter’s allegations had not been substantiated.

Reached at their home Monday night, Darci Kistler, Martins’s wife, told The Washington Post that Martins had no comment on the matter.

According to the New York Times, Martins said in response to the accusations, “The company has already addressed it.” Asked if he had anything to add, he told the Times, “At this point, no.”

Martins is ballet master in chief of NYCB — the top job that most companies call artistic director — and is artistic director and chairman of faculty at SAB.

In a recent interview with The Post, Wilhelmina Frankfurt, a former NYCB dancer, said she was among the SAB alumni called in to meet with SAB Executive Director Carrie W. Hinrichs shortly before Thanksgiving to discuss the investigation. She said she was contacted after Hinrichs saw an article Frankfurt wrote in 2012, which Frankfurt recently posted on Facebook.

In it, Frankfurt compares Martins to NYCB founder George Balanchine: “As a dancer, Peter Martins was a magician. To see him dance was to forgive him everything. But as a Dance Master? The only way that Peter rivaled Mr. B was as a casanova. However, where Mr. B. was charm incarnate, Peter was a basher.”

Frankfurt said Hinrichs told her, “It’s come to our attention that there’s been sexual misconduct on a very high level at our school.” Frankfurt said she was also told that the investigative team includes Kay Mazzo, co-chair of faculty; SAB Chairman Barbara M. Vogelstein; and a lawyer, and that the team was seeking dancers who have knowledge of misconduct.

In 1992, Martins was charged with third-degree assault against his wife, Kistler, who at that time was a 28-year-old principal ballerina with the company. The charges were made while the company was performing at its summer home in Saratoga Springs, N.Y. Martins was arrested and briefly jailed after Kistler called the police early one morning to report that during an argument, Martins, then 45, had pushed and slapped her so that she fell into another room and cut her ankle and that he had continued to hit her.

The arrest was front-page news, with headlines such as this one in the New York Daily News: “BALLET BULLY: NYC Ballet boss busted in beating of ballerina wife.”

Ballet officials immediately downplayed the assault charge. Peter Wolff, a member of the school’s board of directors at the time, told the New York Times that the assault charge was “a personal matter” and would not affect Martins’s career.

“It has nothing to do with his competency or his support in the ballet community,” Wolff said then.

At the time, Martins and Kistler declined to comment.

A few days later, Kistler dropped the charges.

This story has been updated.