An Associated Press investigation has found that more than a dozen U.N. aid workers deployed to deal with the humanitarian crisis caused by five years of civil war in Yemen are being accused of graft, joining with combatants on all sides to enrich themselves from an international outpouring of donated food, medicine, fuel and money.

The AP obtained U.N. internal investigative documents, and interviewed eight aid workers and former government officials. The upshot: internal auditors from the World Health Organization (WHO) are investigating allegations that unqualified people were placed in high-paying jobs, hundreds of thousands of dollars were deposited in staffers' personal bank accounts, dozens of suspicious contracts were approved without the proper paperwork, and tons of donated medicine and fuel went missing.

Critics of such corruption say it threatens the international lifeline on which the majority of Yemen's 30 million people rely. Last year, the U.N. said international donors pledged $2 billion for humanitarian efforts in Yemen. Under WHO rules, aid money can be transferred directly into the accounts of staffers, a measure meant to speed up the purchasing of goods and services in a crisis. The WHO says the arrangement is needed to keep operations going in remote areas because Yemen's banking sector is not fully functioning.