ADDIS ABABA, Ethiopia (AP) — The United Nations food relief agency is investigating the theft of food aid from lifesaving humanitarian operations in Ethiopia, according to a letter obtained by The Associated Press.

The World Food Program’s Ethiopia director, Claude Jibidar, says in the letter that “WFP is very concerned about the large-scale sale of food in some markets” which “poses not only a reputational risk but also threatens our capacity to mobilize more resources for the needy people."

He adds that it “is therefore imperative that immediate actions be taken to curb ... the misappropriation and diversion of humanitarian food” in the country.

The letter is dated April 5 and addressed to humanitarian partners of WFP in Ethiopia, where drought and internal conflict have left 20 million of the country's 120 million people reliant on aid.

Jibidar asks the partner organizations to share “any information or cases of food misuse, misappropriation or diversion that you are aware of or that are brought to your attention by your staff, beneficiaries or local authorities.”

The letter does not mention any specific cases. However, two aid workers told AP the stolen aid included enough food for 100,000 people and was recently discovered missing from a warehouse in Sheraro, a town badly affected by the conflict in Ethiopia’s northern Tigray region. The aid workers spoke on condition of anonymity because of the sensitivity of the matter.

It was not clear who was responsible for stealing the aid from the Sheraro warehouse, which was previously looted by Eritrean soldiers allied to Ethiopia’s federal government in a separate incident. One of the aid workers said it was supplied by USAID and due to be distributed by partners.

In an emailed statement, USAID said it "has proactively identified recent diversion of some of our assistance in Northern Ethiopia.”

“We are in regular communication with our implementing partners regarding incidents of reported diversion and continue to monitor developments closely and take all necessary steps to stop the diversion,” the agency added.

A peace deal signed by the federal government and its Tigray rivals in November has seen restrictions eased and aid deliveries have resumed to the region, where 5.2 million people need humanitarian help.

U.S. Secretary of State Antony Blinken announced $331 million in funding for aid agencies working in Ethiopia during a trip to the country last month.