One of Helen Clark's former ministers says suggestions she's a ruthless careerist are just "sour grapes".
An article published in Foreign Policy magazine has claimed Ms Clark has ended the careers of underlings in her bid for the United Nations' top job. Ms Clark herself has called the allegations "totally fabricated", and Labour's deputy leader Annette King says it's all rubbish.
"It sounds like a disgruntled person who hasn't got what they want, because that's not my experience [with Ms Clark at all]."
Ms King served handled the health, police, transport and justice portfolios under Ms Clark's leadership in the previous Labour-led Government.
After leaving office at the end of 2008, Ms Clark went on to lead the UN Development Programme and earlier this year announced her intention to run for Secretary-General. She has a tough fight ahead of her, with convention dictating it's the turn of eastern Europe to provide a leader.
Left-wing political commentater Chris Trotter says he always expected the dirt to start flying.
"She's going for the preeminent diplomatic post on Earth -- this is not going to be a Sunday school picnic. There's a real fight going on for the job of UN Secretary-General and Helen Clark rates as the frontrunner."
Though she might lead the race, Ms Clark can't ignore the allegations, says Mr Trotter.
"When you throw mud some of it inevitably sticks, so she's going to have to counterpunch quite forcefully to undo the damage that has undoubtedly been done."
The man who replaced her as Prime Minister, John Key, has been supportive of her bid to lead the UN.