After the report was completed, Lena Sinha, who had held a position at the UNDP for 15 years, was told she would "never work for the UNDP again", according to Foreign Policy.
In a statement published on the UNDP website, Clark completely rejected the central claims in the article.
"The recent allegations of retaliation or involvement in a former UNDP staff member's employment status are totally fabricated, as are the allegations regarding the Petrie Report and Human Rights Up Front", she said.
Clark also defended her record on human rights.
"Helen Clark's 40 plus years in public service in New Zealand and at the United Nations speaks for itself. She has advocated and fought tirelessly for the poor and the marginalized, and has always been on the frontlines of human rights."
Clark is considered a front-runner among the nine candidates for the UN secretary-general position, which is being vacated by Ban Ki-Moon at the end of the year. The New Zealand Government is supporting her bid for the role.
New Zealand First leader Winston Peters said he had not found Clark ruthless during his time working with her.
"If they [people who left the UN] deserved to be mercifully ended, she is doing her public job, isn't she ... the reality is, you have to make decisions in the public interest and the public good, then you have to make them."