UNITED NATIONS — The U.N. chief has fired the head of the U.N. peacekeeping mission in the Central African Republic over the force’s handling of dozens of sexual and other misconduct allegations, including rape and killing, in the year and a half of its existence.

Secretary-General Ban Ki-moon, speaking with unusual force, said Wednesday he has accepted the resignation of Babacar Gaye of Senegal and declared, “Enough is enough.” He has called a special session of the U.N. Security Council for Thursday over the issue of sexual abuse allegations that has rocked the world body.

“I cannot put into words how anguished and angered and ashamed I am by recurrent reports over the years of reports of sex abuse and exploitation by U.N. forces,” said Ban, who first heard about the latest allegations Tuesday, a week after the first U.N. officials were informed. “I will not tolerate any action that causes people to replace trust with fear.”

He said he also will hold a special meeting Thursday with the heads of all peacekeeping missions around the world to stress their responsibilities to “report allegations immediately, investigate thoroughly and act decisively.”

Ban’s spokesman, Stephane Dujarric, called the firing of such a high-level official “unprecedented.” He said the peacekeeping force in Central African Republic has faced 57 allegations of possible misconduct, including 11 cases of possible sexual abuse, since the mission was established in April 2014 to calm deadly violence between Muslims and Christians. Ban appointed Gaye in July.

Dujarric said he did not immediately know how many peacekeepers are involved in the 57 allegations.

Gaye did not respond to requests for comment. His resignation letter, seen by The Associated Press, says the problem goes beyond one U.N. mission and likely will continue. “Going forward, you may wish to consider that there could be a systemic problem warranting consideration at the highest level of the organization,” he wrote.

Gaye’s letter also said he had taken a “very robust stand” against misconduct and that his mission had repatriated “many” peacekeepers for misconduct. U.N. officials did not immediately say how many have been sent home.

Ban agreed that the problem of sexual abuse and exploitation by peacekeepers is not limited to one mission. “Sexual exploitation and abuse is a global scourge and a systemic challenge that demands a systemic response.” He urged victims to come forward and not be ashamed: “Shame belongs to the perpetrators.”

The firing comes a day after Amnesty International accused U.N. peacekeepers in Central African Republic’s capital of indiscriminately killing a 16-year-old boy and his father and raping a 12-year-old girl in separate incidents this month.

That follows allegations that U.N. peacekeepers had sexually abused street children in Bangui and a separate allegation of child sexual abuse against a peacekeeper in the eastern part of the country.

In an email Wednesday, the legal director of Medecins Sans Frontieres, Francoise Bouchet-Saulnier, said that “since September 2014, MSF has treated a total of four minors who reported sexual abuse by U.N. peacekeeping forces in three separate cases” in Central African Republic. That includes the 12-year-old girl in the latest allegations.

The U.N., however, has no powers of criminal investigation or prosecution, leaving it up to peacekeepers’ home countries — which U.N. officials often don’t name publicly.

The U.N. mission in Central African Republic is also being investigated over how it handled child sexual abuse allegations against French troops last year, in which children as young as 9 said they had traded sodomy and oral sex for food. Ban said he was looking forward to the independent panel’s findings soon. French authorities are also investigating, but asked Tuesday about their work, Dujarric said, “It is not for us to ask for an update.”

In a statement, the U.S.-based advocacy group AIDS-Free World blasted what it called the “monumental failure of leadership and appalling mismanagement” at U.N. headquarters. The group said peacekeeping mission chief should be fired every time sexual abuse or exploitation by a peacekeeper occurs.

Dujarric told reporters that Ban continued to have “full confidence” in U.N. peacekeeping chief Herve Ladsous, who is currently on holiday.

Ban in the past has expressed his interest in starting to “name and shame” the countries whose peacekeepers are accused of misconduct, though calling out countries has its risks. The U.N. has no standing army and relies on member states to contribute troops and police for its missions.

“I want member states to know that I cannot do this alone,” Ban said Wednesday. “They have the ultimate responsibility to hold individual uniformed personnel to account.”

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Associated Press writer Edith M. Lederer at the United Nations contributed.