The WFP cited reports that aid was being diverted. Its announcement follows a similar one by the US Agency for International Development, which said on Wednesday it had discovered that food intended for people in Tigray was being diverted and sold in local markets.
The UN food agency called on its partners to monitor and report any illicit activities, as well as ensure they enforce agreed controls, Reuters reported on Wednesday.
It did not say who was responsible for the diversions or when they had taken place.
A two-year war that erupted in November 2020 between the federal government and forces led by the Tigray People's Liberation Front, which dominates the northern region, killed tens of thousands of people, created famine-like conditions for hundreds of thousands and displaced millions.
The government and Tigray forces agreed to end hostilities in November, which has allowed additional aid to reach the region, as well as the restoration of some services.
There has been no major return to fighting after the signing of the peace deal.