UN investigators said on Monday that during the 2014 Gaza conflict, Israel and Palestinian militant groups committed grave abuses of international humanitarian law that may amount to war crimes.

They called on all sides to cooperate with the International Criminal Court, which has opened a separate preliminary investigation. The Palestinian Authority is expected to make its first formal submission to The Hague-based court this week.

"The most that we can hope for out of this long and arduous process of inquiry is that we will push the ball of justice a little further down the field," Mary McGowan Davis, chairwoman of the UN commission of inquiry, said at a news conference.