One advocacy group said on Thursday it had passed on new reports to the UN that a soldier made four girls have sex with a dog.
The UN said on Thursday it was investigating 108 new reports of abuse.
Last year, there were 69 allegations of child rape and other sexual offences by peacekeepers from 10 missions.
Forces were deployed in 2014 to help restore order in CAR after the president was overthrown the previous year and sectarian violence gripped the country.
Living under a shadow of fear
Road to anarchy
The new reports of abuse were made by the Code Blue campaign run by the advocacy group Aids-free World. The group says the abuse was reported to have happened between 2013 and this week.
It says the bestiality claims, dating back to 2014, involved a commander with French forces. The girls, one of whom later died of an unknown disease, were each paid 5,000 Central African francs ($8.60; £6), the report says.
UN human rights chief said the countries of the soldiers reportedly involved - France, Burundi and Gabon - had been notified.
"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 on Thursday.
He said the "vast majority" of the 108 alleged victims interviewed by the UN so far were minors. He said the allegations of forced bestiality had not yet been substantiated.
France's ambassador to the UN, Francois Delattre, said the reports were "sickening and odious" and promised exemplary disciplinary action" if they were proven to be true.
A UN statement on Wednesday said the allegations involved some of its staff, as well as non-UN peacekeepers.
In early March, the UN Security Council adopted a resolution calling for the repatriation of peacekeeping units whose soldiers face allegations of sexual abuse.
Last August, the UN envoy to CAR, Babacar Gaye, was sacked amid multiple allegations of sexual abuse by peacekeepers.
An independent panel called the UN response to the allegations "seriously flawed" and a "gross institutional failure".
It accused senior UN officials of abusing their authority by failing to take action over allegations of abuse by soldiers from France, Equatorial Guinea and Chad.
UN chief Ban Ki-moon was "shocked to the core" by new claims of sexual abuse by peacekeepers in the Central African Republic (CAR), the organisation said.