The United Nations says more than 150 women in the Democratic Republic of Congo were raped during a two-day attack in South Kivu province this month.

In a statement Thursday, the U.N.'s special representative on combating sexual violence, Margot Wallstrom, blamed the attack on undisciplined Congolese security forces.

She said former rebels in Congo are integrated into the national army without vetting or systematic training. She added that when the forces are denied adequate pay or provisions, there is a higher risk they will commit crimes.

Wallstrom said the rapes are another “tragic illustration” of the need for security sector reform in Congo.

She also said the United Nations is identifying ways to support the victims.

A medical aid group, Doctors Without Borders, first reported the rapes earlier Thursday, saying they took place around the town of Fizi on June 10 through June 12.

United Nations officials have previously called Congo “the rape capital of the world.” They say an atmosphere of impunity allows soldiers, rebel fighters, and civilians to rape women and children without fear of arrest.

Last month, Congo asked the United Nations to withdraw its peacekeepers and allow the country to take over its own security, saying the country has made significant progress in reducing threats to the safety of citizens.

There are currently 20,000 U.N. peacekeepers in Congo.