UNITED NATIONS - Another United Nations peacekeeping contingent serving in the Central African Republic is suspected of sexually abusing street children in Bangui, a UN spokesman said.

It was the third case of alleged child sexual abuse to have surfaced in recent months involving UN troops.

The UN mission in Bangui has notified the troop-contributing country of the allegations and has opened an investigation, said Mr Stephane Dujarric.

The country of origin was not identified, but a UN official said it was an African contingent.

"Medical care and assistance is now being provided to the alleged victims," Mr Dujarric told reporters in New York. "What we know is that the crimes could go back as far as 2014 and then most recently occurred this year."

"If the allegations are substantiated, this would constitute a grave violation of UN principles and of the code of conduct of peacekeepers."

The "member-state will be requested to take swift and appropriate punitive action", he added.

The country involved had started an investigation and was expected to report back to the UN "as quickly as possible", he said.

Punishment for crimes committed by UN peacekeepers is the responsibility of the country they come from.

Earlier this month, the UN mission in the Central African Republic, known as Minusca, said it was investigating a separate allegation that a peacekeeper had sexually abused a girl in the country's east.

A UN report by rights investigators last year detailed testimony from children in the Central African Republic who said they were sexually abused by French troops and soldiers from Chad and Equatorial Guinea.

France announced last month that 14 soldiers were facing possible charges in the case that came to light only when The Guardian newspaper reported it in April.

Those soldiers were not UN peacekeepers as the United Nations did not take over the African Union operation until September last year. But the UN has been criticised for its slow handling of those allegations.

UN Secretary-General Ban Ki Moon has appointed former Canadian Supreme Court judge Marie Deschamps to head an external independent review into how the world body handled allegations of sexual abuse of children by French and African soldiers.

There are 10,000 UN peacekeepers in the Central African Republic, where violence erupted in 2013 after mostly Muslim Seleka rebels seized power, sparking reprisal attacks from Christian militia.

AGENCE FRANCE-PRESSE, REUTERS