Speaking ahead of the Pacific Leaders Forum next week, Nauru's President Baron Waqa said he blamed advocates for the self-harm incidents.
He told Sky News he is concerned self-harm is being used as a tactic for people to get to Australia.
"We are investigating a lot of these incidences," he said.
"These kids are lovely kids, you know, they roam around, they play around and next thing you hear something terrible. It's the way of working the system and probably short-circuiting it just to get to Australia."
Lawyer George Newhouse, who has acted for child refugees, said the remarks by President Waqa are out of line.
"The President of Nauru was not qualified to make medical assessments and his approach to children with diagnosed illnesses is putting their lives at risk," he said.
A report released by the Asylum Seeker Resource Centre earlier this week found there has been a rise in the cases of mental health condition known as Traumatic Withdrawal Syndrome (TWS), or Resignation Syndrome.
Many advocates and health professionals have warned that refugee children on Nauru are facing an unprecedented health crisis and are at a real risk of death.
“These conditions are increasing as a direct result of prolonged detention, limited access to child and
adolescent mental health care, and severe stress in families," Dr Newman said.
"Children are at the end of their capacity to withstand the trauma of this situation.”
She urged immediate intervention.
“To dismiss the serious nature of mental illness in children is dangerous as well as morally unconscionable," she said.
“What is needed is an urgent response to this unsustainable situation and an immediate amnesty for children and families to access appropriate medical and psychiatric treatment.”
Of the 900 refugees and asylum seekers on Nauru, 119 are children.
World Vision last month released images showing the living facilities were in such a state of disrepair that children were suffering from respiratory problems and skin conditions.
Mouldy tents and dirty bathrooms were removed earlier in the week, and the children relocated to other settlement areas, ahead of the Pacific Island Forum this weekend.
Leaked files seen by the ABC show incident reports from June 2018, including one which documented the use of "sharp metal objects" by a 10-year-old.
Whistleblower and former child psychologist Vernon Reynolds who worked on the island for nearly two years until April 2018 said he feared children could die.
"I'm reasonably surprised that no-one has... I certainly hope that nothing fatal happens. I am deeply concerned that we will see that," he told the ABC.
Mr Reynolds was employed to work at Nauru's detention facility by the Australian government's contractor, International Health and Medical Services (IHMS).
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