The prosecutor of the International Criminal Court in The Hague has asked it to rule on whether it has jurisdiction over the mass deportations of Rohingya from Myanmar to Bangladesh.
The main reason for doubt over jurisdiction is that, while Bangladesh is a member of the court, Myanmar is not.
Prosecutor Fatou Bensouda said forced displacement across an international border could potentially be classed as a crime against humanity.
"This is not an abstract question but a concrete one, affecting whether the court may exercise jurisdiction ... to investigate and, if necessary, prosecute," Ms Bensouda said.
She argued that, given the cross-border nature of the crime of deportation, a ruling in favour of ICC jurisdiction would be in line with established legal principles.
But she acknowledged uncertainty around the definition of the crime of deportation and limits of the court's jurisdiction.
Her request is the first of its kind filed at the court.
The magistrate assigned to consider the request, Congolese judge Antoine Kesia-Mbe Mindua, will have considerable leeway in determining how to proceed.
According to the United Nations, some 700,000 mostly Muslim Rohingya fled their homes into Bangladesh after militant attacks in August last year triggered a military crackdown that the United Nations has said constitutes ethnic cleansing.
Buddhist-majority Myanmar rejects that charge, saying its forces have been waging a legitimate campaign against Rohingya who attacked government forces.