The police believe they have uncovered a plot to kidnap guards at Hawke's Bay Regional Prison.
In June the jail was the scene of two protests, one where inmates broke through the ceiling of a unit and made a stand on the prison roof.
Two 17-year-olds from the prison's youth unit are accused of seriously assaulting a prison guard, and throwing boiling water over another, on 21 June. They are also accused of wilful damage to the prison wing.
Fresh charges have now been laid by the police, who allege the pair worked together to concoct a plot to kidnap guards.
The police say the plan was relatively unsophisticated, and uncovered by prison staff themselves, but aren't disclosing further details.
The teenagers are due back in court on 9 August.
The police say the incident is separate from the two protests in June, for which charges are still to be laid.
