Hamas leaders on Monday launched an unprecedented attack against President Mahmoud Abbas, saying they no longer consider him a Palestinian after he agreed to suspend efforts to go after Israel for alleged war crimes in Gaza.

The harsh verbal assault is likely to undermine attempts at reconciliation between the Western-backed Abbas and his Islamic militant Hamas rivals, who control the Gaza Strip.

Syria abruptly postponed Abbas' planned visit to Damascus in what appeared to be the first diplomatic fallout from his decision to suspend a campaign to push for war crimes prosecutions in connection with last winter's Gaza war.

A U.N. report alleged that both Israel and Hamas committed war crimes during the three-week offensive in Gaza, a charge both deny.

The U.S. exerted pressure to delay of the vote, apparently to keep the hope of renewed Mideast negotiations alive. Israel's prime minister warned last week that pursuing war crimes charges would sabotage efforts to restart peace talks.

The U.N. Human Rights Council in Geneva decided last week to put off a vote on the report for six months, rather than refer it to the U.N. General Assembly immediately for possible action.

Abdullah Abdullah, a lawmaker in Abbas' Fatah movement, said Monday that the Palestinian diplomats had been urged by "certain friendly countries" to put off the vote.

The decision sparked outrage across a wide swath of Palestinian society.

In Gaza, Hamas leader Mahmoud Zahar said Monday that Abbas and others involved in the decision should be shunned. "We don't consider them Palestinians or representatives of the Palestinian people," Zahar said.

Hamas drove Abbas' forces out of Gaza in 2007, leaving him in control of only the West Bank. Repeated reconciliation efforts have failed, complicating peace efforts with Israel.

Egyptian mediators have asked Hamas and Fatah to return to Cairo for another round of talks later this month, and it appeared Hamas was using the domestic backlash against Abbas as leverage.

"I ask how the different parties can sit at the same table given this situation? How can the proper environment be created, given this unprecedented renunciation, this sacrifice of the martyrs' blood and our people's rights?" Gaza's Hamas prime minister, Ismail Haniyeh said Monday.

Syria called off the Abbas visit, a Syrian official said Monday, refusing to give a reason. However, the cancellation came just a day after Syria criticized the Palestinian Authority for backing down on the war crimes issue. Abbas' visit was set to begin Tuesday.

Abbas adviser Nabil Abu Rdeneh said there had been a "technical change" in the president's schedule.

In the West Bank city of Ramallah, several hundred protesters marched in the central square, calling for the resignation of those who took the decision. "Listen, listen, Abbas, our people's blood is not spilled in vain," they chanted.