UN Secretary-General Ban Ki-moon is “shocked to the core” by allegations of sexual abuse by UN peacekeepers and French troops in the Central African Republic, his spokesman said Thursday.

“We must face the fact that a number of troops sent to protect people instead acted with hearts of darkness,” UN spokesman Stephane Dujarric said.

The United Nations is investigating new claims that troops from Burundi and Gabon serving in its peace force in the Central African Republic sexually abused women and girls.