The United Nations peacekeeping contingent serving in the Central African Republic are accused of sexually abusing street children in Bangui, a UN spokesman has said.
UN Secretary-General Ban Ki-moon's spokesperson, Stephane Dujarric, said the latest incident was the third case of alleged child sexual abuse involving peacekeepers in the CAR to have surfaced in recent months.
"If the allegations are substantiated, this would constitute a grave violation of UN principles and of the code of conduct of peacekeepers," Dujarric said on Tuesday.
The UN mission in Bangui has notified the troop-contributing country of the new allegations and has opened an investigation, Dujarric said.
The country of origin was not identified, but a UN official said it was an African contingent.
The "member-state will be requested to take swift and appropriate punitive action", he added.
In the wake of previous cases, the UN MINUSCA force asked Morocco to open a formal investigation after allegations that one of its soldiers raped a girl under the age of 16.
A UN report by rights investigators last year detailed testimony from children in CAR who said they were sexually abused by French troops and soldiers from Chad and Equatorial Guinea.
The sexual abuse allegedly took place from December 2013 to June 2014, a few months before the UN took over from the African Union mission with its MINUSCA force.
Read more: UN releases report on sex abuse by peacekeepers
Last week, a UN report said that South African soldiers face the most accusations of sexual abuse while on UN peacekeeping missions.
The UN said it had received 480 allegations of sexual exploitation and abuse relating to its peacekeeping and special political missions between 2008 and 2013, with South African troops facing the most allegations of abuse.
The report showed that South African troops faced nine allegations, followed by Uruguay with eight allegations and Nigeria with seven allegations. The details of the allegations were not given.
France announced last month that 14 soldiers were facing possible charges in the case that only came to light when The Guardian newspaper reported it in April.
In the most recent case, MINUSCA received allegations on June 19 that two girls under age 16 had been sexually abused in Bangui, a UN official said.
The girls, who have been offered medical assistance, told a local rights group that they received food and goods in exchange for sex and that the abuse started in 2014.
The troop-contributing country was notified on Monday of the allegations and given 10 days to advise the United Nations on the measures that it intends to take in response to the serious claims.
Under UN rules, military personnel serving in peace operations face possible prosecution at home.
Ban, on Monday, appointed a three-member panel to review how the UN handled the child sexual abuse allegations in the CAR.
Former Supreme Court justice of Canada Marie Deschamps will lead the review that is expected to begin work next month, with a final report to be submitted within 10 weeks.
An internal UN report revealed this month that UN blue helmets routinely buy sex with jewellery, mobile phones and televisions in countries where they are deployed.
The UN has 125,000 peacekeepers deployed in 16 missions worldwide.
The MINUSCA force was deployed in September, taking over from the AU force that had been sent to help restore order after the country exploded into violence following a coup.