Medicins Sans Frontieres (MSF) has apologised after reports emerged of sexual harassment and misconduct by its aid workers.
Whistleblowers told the BBC’s Victoria Derbyshire programme that MSF staff working in Africa used local prostitutes.
The programme spoke to eight whistleblowers overall, with many also saying they had experienced sexual harassment towards female MSF employees.
A former employee at the charity's London office said she had seen a senior member of staff bring girls back to MSF accommodation while posted in Kenya.
"The girls were very young and rumoured to be prostitutes," she said. "My colleague, who was staying in the same residence for a long time, felt that this was a regular occurrence.”
The whistleblower said she and her colleague felt unable to challenge the man "because he was quite senior" and deemed “too big to fail”.
Another female whistleblower, who worked with HIV patients in central Africa, said the use of local sex workers was "blatant and widespread".
"There was an older colleague who actually moved a woman into the compound [where MSF staff were staying]," she said.
"It was pretty obvious she was a prostitute but he called her his girlfriend and she would spend night after night with him.”
She also said she felt sexually harassed by some of the men she worked with, including one colleague who deliberately left condoms in her room while she was away.
The whistleblower said she had reported his behaviour to her boss in the field and had been offered mediation, but had also been told she would be fired if she did not sort things out with her colleague.
A third whistleblower said a senior colleague had claimed that it was possible to barter medication for sex.
"He was suggesting lots of the young girls who had lost their parents to the Ebola crisis would do anything sexual in exchange for medication,” she said.
She said he had bragged about it "quite a lot", in front of three or four people who had been working in Liberia themselves and to her directly.
She also said MSF workers had sexually harassed employees at MSF’s partner NGOs, including telling one woman “how sexy she was... asking her where her husband was”.
MSF said it was unable to confirm the specific allegations made in the BBC report but said it was sorry for “any instances where people have been subjected to harassment, abuse or otherwise mistreated and/or felt that it was not adequately dealt with”.
The charity expressed regret that the whistleblowers had not felt able to voice their concerns directly to MSF.
It said: “Underreporting is a key challenge as those affected may not come forward for fear of not being believed or being stigmatised. Unfortunately this is as true in MSF as it is in wider society.
We continue to improve our reporting mechanisms so people feel safe to report abuse at MSF, and to ensure that all staff understand the importance of responsible behaviour and conduct themselves in a responsible manner. We have sanctioned people for misconduct, including dismissal.”
It added: "We do not tolerate abuse, harassment or exploitation within MSF."