The UN secretary-general has fired the head of the UN peacekeeping mission in the Central African Republic over the force's handling of a series of misconduct allegations, including rape and killing.

Ban Ki-moon, speaking with unusual force, said on Wednesday he has accepted the resignation of Babacar Gaye of Senegal and declared, "Enough is enough." He called a special session of the UN 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 UN forces," said Ban, who first heard about the latest allegations on Tuesday, a week after the first UN officials were informed. "I will not tolerate any action that causes people to replace trust with fear."

He was scheduled to hold a special meeting on 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.

The problem of sexual abuse and exploitation by peacekeepers is not limited to one mission, the UN chief said. "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 human rights activists accused UN 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 UN 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 e-mail on Wednesday, the legal director of Doctors Without Borders, Francoise Bouchet-Saulnier, said that "since September 2014, MSF has treated a total of four minors who reported sexual abuse by UN peacekeeping forces in three separate cases" in the country.

The UN 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 on Tuesday about their work, Dujarric said, "It is not for us to ask for an update."