Helen Clark says allegations that she retaliated against a critical investigation of the United Nations by driving one of the investigators out of their job are "totally fabricated".
The former New Zealand Prime Minister and leading candidate for the UN's top job also said other revelations in a Foreign Policy article published overnight were made up.
The article said that while there was strong popular support for Clark to take on the job, "many of her own UN colleagues are not rooting for her".
Clark's seven-year tenure in charge of the UN Development Programme (UNDP) had "left a trail of embittered peers and subordinates", Foreign Policy said. Her UN colleagues had accused of her of "ruthlessly ending the careers of underlings in her quest to advance her candidacy and of undercutting the UN's promotion of human rights".
The most serious allegation was that Clark's senior staff had forced out American-Swedish UN official Lena Sinha after she had participated in an investigation which was critical of the UNDP's response to mass atrocities in Sri Lanka.
The investigation, called the Petrie Report, criticised senior members of Clark's agency, saying that they had downplayed the Sri Lankan Government's role in killing thousands of Tamils.
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."