Radio NZ reported Jacinda Ardern as saying:
I believe mistakes were made
Wikipedia has an interesting page on that phrase:
“Mistakes were made” is an expression that is commonly used as a rhetorical device, whereby a speaker acknowledges that a situation was handled poorly or inappropriately but seeks to evade any direct admission or accusation of responsibility by not specifying the person who made the mistakes. The acknowledgement of “mistakes” is framed in an abstract sense, with no direct reference to who made the mistakes. A less evasive construction might be along the lines of “I made mistakes” or “John Doe made mistakes”. The speaker neither accepts personal responsibility nor accuses anyone else. The word “mistakes” also does not imply intent.
The New York Times has called the phrase a “classic Washington linguistic construct.” Political scientist William Schneider suggested that this usage be referred to as the “past exonerative” tense, and commentator William Safire has defined the phrase as “[a] passive-evasive way of acknowledging error while distancing the speaker from responsibility for it“. A commentator at NPR declared this expression to be “the king of non-apologies“.[3