JOHANNESBURG — Nobel Peace Prize winner Desmond Tutu said Thursday he will no longer be a global ambassador for the British-based aid organization Oxfam after allegations that senior staff members in crisis zones paid for sex among the desperate people the group was meant to serve.

A statement from the office of the South African former archbishop said he was “deeply disappointed by allegations of immorality and possible criminality.”

Tutu’s office said it had written to Oxfam “to inform them of his retirement as a global ambassador.”

The 86-year-old Tutu rarely makes public statements because of health problems.

British actress Minnie Driver and Senegalese musician Baaba Maal also have quit as a celebrity ambassadors for Oxfam.

The charity is reeling from allegations that senior staff members working in Haiti after the country’s 2010 earthquake faced misconduct allegations that included using prostitutes and downloading pornography.

Oxfam says it investigated the allegations at the time, but the British government and charity regulators have criticized its lack of transparency.

U.K. International Development Secretary Penny Mordaunt has warned that government funding to the group — some 31.7 million pounds ($43.8 million) in 2016-17 — is at risk unless it comes clean about the allegations.

Mordaunt met Thursday with the head of Britain’s National Crime Agency, amid fears that sex predators have targeted aid organizations to get access to the vulnerable.

After the meeting the crime agency said officials would work “to protect vulnerable people and ensure appropriate safeguarding provisions are in place for organizations involved in overseas aid.”