The International Criminal Court on Wednesday dismissed an appeal against a decision not to probe Israel over a deadly raid on an aid flotilla to Gaza in 2010.
Nine Turkish citizens died when when they attacked Israeli commandos as they boarded the Mavi Marmara ship, which was trying to breach the embargo on Gaza. One more died in hospital in 2014.
The Hague-based tribunal's prosecutor Fatou Bensouda found in December there was no basis to proceed with a full investigation.
The Comoros, the Indian Ocean nation where the ship was registered and which made the original complaint, had challenged that decision.
ICC judges said on Wednesday that the court "rejects Comoros' request for judicial review of the prosecutor's decision not to open an investigation".
The judges claimed that Bensouda made "errors" in an original 2014 decision not to investigate.
They also said she did not "genuinely reconsider" that decision as the court had ordered, and then made further mistakes before she decided again, in 2019, not to probe the case.
But the judges said it was "unclear" what powers they had to ask the prosecutor to fix the mistakes, and so they were unable to ask her to further review the case.
The ICC was set up in 2002 to deal with war crimes and crimes against humanity.