The International Criminal Court (ICC) on Tuesday said it had detected unusual activity on its information systems at the end of last week.
"Immediate measures were adopted to respond to this cybersecurity incident and to mitigate its impact," the ICC said in a statement.
A spokesperson for the court said they could not comment on matters such as how the hack took place, to what extent operations were impacted or who might be behind it.
The ICC is the permanent war crimes tribunal in The Hague, established in 2002 to prosecute war crimes and crimes against humanity.
The court said in its statement that it was continuing to "analyse and mitigate the impact of this incident" with the assistance of the Dutch government.
It said it was also taking steps to strengthen its cybersecurity.
