The federal government has announced a further inquiry into children in detention on Nauru,

The immigration minister, Scott Morrison, confirmed 10 employees of Save the Children, a non-government organisation contracted to provide welfare, education and protection for children on Nauru, had been told to leave the island.

Morrison has appointed former integrity commissioner and acting department head Philip Moss to head the wide-ranging inquiry investigating “all of these matters”.

The 10 staff members told to leave Nauru are not alleged to have engaged in misconduct against children, but are accused of encouraging protests, complaints of abuse and even of coaching self-harm.

The chief executive of Save The Children, Paul Ronalds, rejected the minister’s allegations and said the governmement had not provided his organisation with any evidence of staff wrongdoing before the claim was leaked to the media, or since.

Nor had it received the report cited by Morrison.

Five Save The Children staff were suspended in August over allegations they had supported a detainee protest by giving a “thumbs up” sign to demonstrators.

“In that case, all of the allegations against Save the Children staff were found to be unsubstantiated, and all of the staff returned to full duties,” Ronalds said.

Save the Children said in an earlier statement instances of child self-harm were “a reality that has been well-documented”.

“The evidence is very clear to us: the long-term and prolonged detention of children has a devastating impact on the mental and physical well-being of children. This can no longer be denied.”

Morrison said he would be appalled if accusations of sexual abuse proved true, but that the fabrication of allegations to further a political agenda was also serious.

Guardian Australia has published extensive evidence of child abuse and instances of self-harm on Nauru, including:

• pictures and video of children with their lips sewn shut in protest
• internal reports from centre managers Transfield detailing allegations of sexual misconduct by staff against children
• detailed descriptions from staff about violence against child detainees by guards employed by Wilson Security.

Australian federal police confirmed to Guardian Australia it had received a referral from the Department of Immigration and Border Protection. It had not started an investigation.