WELLINGTON (Reuters) - New Zealand Prime Minister Jacinda Ardern said on Monday an independent reviewer will look into her party’s handling of sexual assault complaints against a party staffer, amid mounting pressure and questions about her leadership on the matter.

FILE PHOTO: New Zealand's Prime Minister Jacinda Ardern is seen at the Istana in Singapore, May 17, 2019. REUTERS/Feline Lim

Ardern apologized to the 19-year-old complainant last week and took control of the investigation, as the matter became a major embarrassment for the center-left coalition government, led by Ardern’s Labour Party, ahead of a general election next year.

Ardern told a news conference a party lawyer would finish a report on the Labour response to complaints, and it would then be handed to an independent third-party reviewer who would “establish a statement of facts on the party process and what complaints were received”.

“Mistakes have been made ... it’s now my job to address it,” Ardern told the news conference after a cabinet meeting.

“We have a duty of care and we failed in it,” she said.

The woman who complained alleged that last year a party staffer assaulted her in a private residence, and she reported this to the Labour Party, including then party president Nigel Haworth.

The party investigated the matter and concluded that no further action was needed against the party staffer.

But Ardern ordered a review of the matter last month after other complaints came about the staffer, and media reports emerged giving details of the 19-year-old’s account and the nature of the assault.

Ardern accepted Haworth’s resignation and the man accused of the assault, who has not been identified, has also resigned.

Haworth argued that the complainants never informed him about the seriousness of the assault. The man facing the accusations has denied them, media has reported.

Ardern has said she was never made aware that the complaints were sexual in nature. But critics say she acted late and tried to protect colleagues who mishandled the complaints.

Ardern said she was willing to meet the complainants but it would be best if the matter was kept out of the public domain.

Ardern has seen her ratings drop in recent months due to the coalition’s handling of the economy and other issues.