The International Federation of Red Cross and Red Crescent Societies says it has discovered several cases of fraud committed during the height of the Ebola outbreak in West Africa from 2014 to 2016.
In a statement, the aid agency said it was "outraged" by the discovery and would "ensure any staff involved are held to account."
The outbreak killed more than 11,000 people, infected another 29,000 and cost more than $6 million during its height, when it ravaged the countries of Guinea, Sierra Leone and Liberia.
In Sierra Leone, the Red Cross said it had found evidence of "likely collusion" between a bank and former Red Cross employees that resulted in a $2.1 million loss.
In Guinea, overbilling and fake invoices cost the agency about $1.2 million. The Red Cross said two other investigations were underway in Guinea.
And in Liberia, the organization found that inflated prices for relief items and payroll had cost an extra $2.7 million.
The Red Cross said it was committed to holding to account all those involved in the illegal activities, and also to reclaiming all misappropriated, diverted or otherwise illegally taken funds.
The organization, which has undergone past corruption scandals, said that since 2014 it has implemented cash spending limits in "high-risk" settings and has begun deploying auditors when it sends out relief teams.