DAKAR, Senegal (AP) — The United Nations in Chad has launched an internal investigation, following an Associated Press report on allegations of sexual exploitation of Sudanese refugees, which included aid workers.

The statement, written days after the AP published the story last week, was seen on Tuesday. It said the seriousness of the allegations cited in the AP's story, warranted immediate and firm measures and that those responsible should be punished.

“Refugees are already vulnerable and traumatized by the events that led them to flee their country and under no circumstances should they be the victims of abuse by those who are supposed to help them,” said Francois Batalingaya, the U.N. resident and humanitarian coordinator in Chad.

The U.N. did not immediately respond to questions about what the internal investigation entailed.

Earlier this month, the AP reported accusations by some Sudanese women and girls that men, including those meant to protect them such as humanitarian workers and local security forces, had instead sexually exploited them in Chad’s sites for displaced people. They said the men offered money, easier access to assistance, and jobs. Such sexual exploitation in Chad is a crime.

Hundreds of thousands of people, most of them women, have streamed into Chad to escape Sudan’s civil war, which has killed over 20,000 people.

Sexual exploitation during large humanitarian crises is not uncommon, especially in displacement sites. Aid groups have long struggled to combat the issue, citing a lack of reporting by women, not enough funds to respond and a focus on first providing basic necessities.

Experts say exploitation represents a deep failure by the aid community and that people seeking protection should never have to make choices driven by survival.

The U.N. said it raised the risk alert level for protection against sexual exploitation of abuse to four, which is very high, especially since Chad was already classified as a country at high risk. Raising the alert is meant to enable the U.N. to take rapid measures in the next three months, according to an internal email about the AP's article, circulated among aid groups and seen by the AP.

The UN said it's cooperating with local authorities and human rights groups to hold those responsible to account and that refugees’ trust in humanitarians is paramount.

The organization has encouraged anyone with information about exploitation to come forward.