The rare meeting of the Palestinian Central Council - a high-ranking arm of the Palestine Liberation Organisation - was called after Trump's controversial December 6 recognition of Jerusalem as Israel's capital.
Palestinians want the annexed eastern sector of the city as the capital of their future state, and president Abbas has said Trump's stance means the US can no longer be the mediator in peace talks with Israel.
Speaking late yesterday at the opening of the council, which brings together Palestinians from multiple political parties, Abbas told delegates: "We said 'no' to Trump, 'we will not accept your project.'"
"The deal of the century is the slap of the century and we will not accept it," the 82-year-old leader added, referring to Trump's pledge to reach the "ultimate deal".
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He instead called for an internationally mediated peace process.
Israel is unlikely to accept any other mediator than the United States, accusing United Nations bodies of systematic bias against it.
The last meeting of the PCC in 2015 called for ending security coordination with Israel, but its decisions were non-binding and it was never implemented.
The Palestinians' relations with the US leadership have deteriorated rapidly since Trump's election.
He came to power promising to lead the most pro-Israel administration in history, but also to pursue a peace deal.
His envoys, including senior adviser and son-in-law Jared Kushner, had been shuttling between the two sides in search of common ground.
But Trump also infuriated the Palestinians by refusing to commit to the idea of an independent Palestinian state, and recently threatened to cut hundreds of millions of dollars in US aid.
Last night, Abbas attacked the US ambassadors to Israel and the United Nations, David Friedman and Nikki Haley, calling them a "disgrace".
Both Trump appointees have been strong supporters of Israel, with Friedman having backed Jewish settlements in the occupied West Bank.
An indignant Abbas also said that Trump had accused them of refusing to engage in peace negotiations.
"May God demolish your house. When did we refuse?" he said, using a common Arabic curse.
In a speech during a visit to India today, Israeli Prime Minister Benjamin Netanyahu did not mention Abbas's comments.
Abbas said all options were on the table for responding to Trump's Jerusalem declaration, but did not specifically mention suspending recognition of Israel or ending security coordination with the Jewish state - both policies mooted in the days before the council.
He did, however, say the Oslo accords that led to the creation of his Palestinian Authority and envisioned a final resolution to the conflict were in effect finished.
In response to Abbas's comments, the European Union said its position on the conflict remains "based on the Oslo accords".
"A negotiated two-state solution which fulfils the aspirations of both sides, Israel and Palestine, is the only realistic way of bringing the lasting peace and security that both Israelis and Palestinians deserve," European Commission spokeswoman Maja Kocijancic told reporters in Brussels.
France, which organised an international conference in support of the two-state solution a year ago, issued a similar reaction, while Russian Foreign Minister Sergei Lavrov said Moscow "understands" Abbas's anger.
"We constantly hear that the US is about to unveil an important deal that would satisfy all sides. We have not seen this kind of document.