According to Reuters, the Hague is currently weighing Britain's claim to Chagos Islands.
Mauritius has been appealing the case to judges at the World Court on Monday.
It says Britain illegally stripped it of the Indian Ocean archipelago.
The Islands are now home to a major U.S. air base.
In 1965 Britain detached the Chagos Islands from its colony of Mauritius.
Mauritius became independent three years later.
The sparsely populated Chagos Islands, however, remained overseas British territory.
The U.S. has leased the biggest island, Diego Garcia, since 1966.
It built an air base there, forcing the population of around 1,500 people to leave.
The case is a test of whether colonial-era deals struck by great powers are legitimate.