Amnesty International and Human Rights Watch urged Palestinian President Mahmoud Abbas on Thursday to promptly seek access for Palestine at the International Criminal Court in The Hague.

The world's two leading human rights NGOs, along with 15 others, mainly Palestinian, said in a letter to Abbas that such a move "could ensure access to international justice for victims of war crimes and crimes against humanity committed on Palestinian territories, and would send an important message that such crimes cannot be committed with impunity."

They noted that the ICC Office of the Prosecutor has ruled that the Palestinian Authority's 2009 decision to accept the court's jurisdiction was marked by "legal invalidity," and that this was not changed by the UN General Assembly's 2012 decision to upgrade Palestine to the status of "non-member observer state. The letter stressed to Abbas that ICC Prosecutor Fatou Bensouda has since said that the ball is now in the court of Palestine to seek the court's jurisdiction by joining the Rome Statute, which established the International Criminal Court.

The signatories wrote that they appreciated that Abbas was under pressure from the United States and Israel, and at times from other Western countries as well, not to go to The Hague.

But they asserted: "We oppose these efforts to politicize justice for victims of serious crimes under international law, and urge you to resist them. The commission of war crimes with impunity has regularly undermined the peace process. A credible prosecution threat would help to advance the cause of peace."

The letter was delivered in Ramallah to chief Palestinian negotiator Saeb Erekat, who said he would give it immediately to Abbas, according to a statement from the Palestine Liberation Organization. Erekat thanked the human rights groups for their tireless work towards the advancement of a just peace for Palestine and Israel, based on respect for human rights and international law. The world must realize that Palestine cannot continue being the exception to the rule.

The move came a day after the former ICC prosecutor, speaking in Israel, advised the Palestinians to proceed with caution as they consider pursuing war crimes against Israel.

Luis Moreno-Ocampo, who is in Israel as a guest of the Fried-Gal Transitional Justice Initiative at the Hebrew University Law School, said on Wednesday that while the Palestinians are eligible to join the court, the move could backfire against them.

Moreno-Ocampo stressed that Gaza's Hamas rulers also could be investigated for rocket fire and suicide bombings against Israeli civilians, if the Palestinians put themselves under the court's jurisdiction. .

He recommended that Israel and the Palestinians avoid the court and find a "creative" way to resolve their differences. He refused to speculate whether war crimes have been committed by either side.