WASHINGTON — The One Campaign, an advocacy organization co-founded by Bono of the rock band U2, is acknowledging “an institutional failure” after an internal investigation revealed a pattern of abuse and misconduct among leadership in its Johannesburg office.

In a letter to members posted on its website Friday, CEO Gayle Smith says that between 2011 and 2015 staffers were bullied, berated and belittled by managers. In one instance, a supervisor made her employees work as party hostesses at her home on weekends.

The letter also says a female employee alleged that a supervisor made sexist and suggestive comments about her to a government official, and that she was demoted after refusing to have sex with the dignitary.

Smith says all employees and managers involved are no longer with the organization.