LONDON — U2’s frontman, Bono, said this weekend he was “furious” after a charity he co-founded was rocked by newly revived accusations that it had fostered an atmosphere of bullying, abuse and, in one case, attempted sexual coercion in its Johannesburg operation.

Bono apologized to the former employees of the charity, ONE, who have detailed on social media and in a British newspaper what they said was demoralizing treatment by managers at their office in the South African city from late 2011 to 2015.

He said the charity, which aims to “end extreme poverty and preventable disease, particularly in Africa,” had failed to protect the workers.

“I need to take some responsibility for that,” Bono said in a statement issued on Saturday and published by The Mail on Sunday. “We are all deeply sorry. I hate bullying, can’t stand it.”