The ICC, which among other things is investigating war crimes in Ukraine, declined to provide further details and said its priority was on ensuring it was able to continue its work.

"At the end of last week, the International Criminal Court's services detected anomalous activity affecting its information systems," the court said in a statement.

"Immediate measures were adopted to respond to this cybersecurity incident and to mitigate its impact," it said.

The court, based in The Hague, is no stranger to international espionage.

The Netherlands said it had stopped a Russian spy posting as a Brazilian intern from infiltrating the court last year.

The Russian, identified as Sergey Vladimirovich Cherkasov, could have accessed "highly valuable" intelligence on the ICC's probe into war crimes in Ukraine or even influenced criminal proceedings, according to Dutch authorities.

The ICC is probing war crimes and crimes against humanity in Ukraine, and issued an arrest warrant for Russian President Vladimir Putin in March over alleged child deportations.

In response, Russian authorities put ICC prosecutor Karim Khan on a "wanted" list.

Khan is speaking later Tuesday on the sidelines of the UN General Assembly about "combating cyber operations in warfare."