The United Nations says investigations are underway into the alleged corruption of World Health Organization personnel over relief aid in Yemen amid years of civil war.

UN spokesperson Stephane Dujarric revealed the news on Tuesday following an AP report that WHO internal auditors are investigating allegations, including dozens of suspicious contracts and suspected diversions of donated medicine and fuel. The WHO is a UN agency.

Dujarric told reporters that his understanding is that the investigation over the alleged misuse of aid is ongoing. He said the WHO is taking the allegations extremely seriously and that the UN has zero tolerance for corruption.

The UN says 16 million people in Yemen, or more than a half of its population, have been suffering from severe food shortages since the civil war started in 2015.

The world body has repeatedly held donors’ conferences to ease what is described as the world’s worst humanitarian crisis.

Donations totaling 1.6 billion dollars have been raised, including 40 million dollars from Japan, to finance aid activities for this year to provide food and medicine across Yemen.