The International Criminal Court (ICC) has ordered its chief prosecutor to review an earlier decision not to open a probe into a 2010 Israeli attack on a Gaza-bound aid flotilla that killed nine Turkish activists.

"The prosecutor (Fatou Bensouda) committed material errors in her determination of the gravity of the potential case(s)," the Hague-based ICC judges said on Thursday.

"In particular, the Chamber identified material errors in the prosecutor's assessment of the possibility to prosecute those persons who may bear the greatest responsibility for the identified crimes committed during the seizure of the Mavi Marmara," the judges added.

Bensouda must now reconsider her decision "as soon as possible and shall notify the Chamber, the Comoros and the victims ... of her conclusion and the reasons for it," the judges said.

On November 6, 2014, Bensouda said publicly available information provided “a reasonable basis” to believe that the Israeli forces committed war crimes during the attack in international waters back in 2010, but the case did not fall under their jurisdiction for an official probe.

Comoros, the tiny Indian Ocean island state, where the Turkish activists' ship, the Mavi Marmara, was registered, later lodged a case, urging ICC judges to review Bensouda's decision.

This TV grab shows Israeli forces on board the Gaza-bound Mavi Marmara aid ship in international waters on May 31, 2010. ©AFP

On May 31, 2010, Israeli commandos attacked the Freedom Flotilla in international waters in the Mediterranean Sea, killing nine Turkish citizens, including a teenager with dual Turkish-US citizenship, on board the Turkish-flagged Mavi Marmara and injuring about 50 other people who were part of the team on the six-ship convoy.

The flotilla was attempting to break the Israeli naval blockade of the Gaza Strip, carrying aid to Palestinians in the enclave.

Gaza has been blockaded since June 2007, which has caused a decline in the standards of living, unprecedented levels of unemployment, and unrelenting poverty.

The attack sparked international outcry and plunged relations between Tel Aviv and Ankara to an all-time low at the time.