The U2 singer, 57, said he was left “furious” after the allegations surfaced in November last year.
He admitted that the ONE organisation failed to protect some employees at its Johannesburg office and said: “I need to take some responsibility for that.”
His comments came as a national newspaper detailed a string of incidents, including allegations from a woman who says she was demoted after refusing to have sex with a Tanzanian MP.
“We are all deeply sorry. I hate bullying, can’t stand it,” he said. “The poorest people in the poorest places being bullied by their circumstance is the reason we set up ONE. So to discover last November that there were serious and multiple allegations of bullying in our office in Johannesburg left me and the ONE board reeling and furious.”
Some former employees have launched legal action against the charity, which aims to tackle poverty and disease, particularly in Africa.
Gayle Smith, ONE’s chief executive officer since March last year, said an investigation found evidence of “unprofessional conduct” as well as “bullying and belittling of staff” between late 2011 and 2015.
“Staff were called names, and some said their manager put them to work on domestic tasks in her home,” she said in a statement.
“The investigation also found the situation was not adequately addressed nor resolved by executive management at the time, and that ONE’s board was not, in my view, properly or fully informed.” She also acknowledged an allegation that a woman was “demoted because she did not become intimate” with an official from another country, but added: “We have not been able to corroborate these appalling claims.”
Bono said that although the allegations focus on one individual, “the head office failed to protect those employees and I need to take some responsibility for that”.