U2 singer Bono has apologised following claims that workers at a charity he co-founded suffered bullying and abuse.

He said he was “furious” over the allegations and admitted that the ONE organisation failed to protect some employees at its office in Johannesburg, South Africa.

The Mail on Sunday reported claims by a woman who said she was demoted after refusing to have sex with a Tanzanian MP.

The singer, 57, told the paper: “We are deeply sorry. I hate bullying, can’t stand it. 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.”

The charity, which aims to tackle poverty and disease in Africa, is facing legal action by former employees.

ONE’s chief executive officer Gayle Smith said an investigation had found evidence of “unprofessional conduct” along with “bullying and belittling of staff” between late 2011 and 2015.

Ms Smith was not CEO at the time of the alleged offences.

In a statement, she said: “Staff were called names, and some said their manager put them to work on domestic tasks in her home.

“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.”

Ms Smith said there had also been 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.

“We do not discount any allegation – we investigate them and will continue to do so should others arise.”