The Samoan judge, who sits in the world's first permanent war crimes court, has urged more states to get behind the new organisation.
It is the first time a sitting judge of the International Criminal Court has spoken out about the organisation's new powers.
The United States has refused to recognise the court, for fear its soldiers may be brought before it, to answer charges of genocide, war crimes, or crimes against humanity.
Judge Tuiloma Neroni Slade, formerly Samoa's ambassador to the United States, told an audience in Wellington last night that, ideally, many more countries will ratify the Rome Statute which sets up the court.
"Let me say on behalf of the court that the Rome Statute must become universal and that the International Criminal Court requires the co-operation and the participation of states. The court cannot be effective by itself. The support it currently enjoys need to be even more widespread and from many more counntries."
Judge Tuiloma Neroni Slade said the court needed to have universality.
He said the court could expand on what he called the 'practical possibilities' opened up by the tribunals set up to deal with alleged war crimes in Rwanda and the former Yugoslavia.
