THE HAGUE: The International Criminal Court opened a formal investigation on Wednesday into alleged war crimes in the Palestinian territories, in a move blasted by Israeli premier Benjamin Netanyahu as the "essence of anti-Semitism".

Palestinian authorities hailed the decision by ICC chief prosecutor Fatou Bensouda as an "urgent and necessary" probe into the situation in the blockaded Gaza Strip along with the Israeli-occupied West Bank and east Jerusalem since June 2014.

The move plunges The Hague-based tribunal -- which has faced frequent criticism by Israel and its ally the United States -- into the midst of one of the world's most bitter conflicts and risks inflaming an already tense situation.

Washington said it was "disappointed", and State Department spokesman Ned Price said the US would "firmly oppose" the move.

Bensouda said she had decided there were "admissible potential cases" on both sides, with the investigation focusing on the 2014 Gaza conflict, which left more than 2,000 people dead.

"In the end, our central concern must be for the victims of crimes, both Palestinian and Israeli, arising from the long cycle of violence and insecurity that has caused deep suffering and despair on all sides," the prosecutor said.

Gambian-born Bensouda said the formal investigation followed a "painstaking" five-year preliminary probe, and vowed it would be conducted "independently, impartially and objectively, without fear or favour."

Israel has refused to sign up to the court, set up in 2002 to try the world's worst crimes, but the Palestinians have been a state party to the ICC since 2015.