AFP-- 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 Al-Quds as Israel's capital.
Palestinians want the annexed eastern sector of the city as the capital of their future state and Mahmud Abbas has said Trump's stance means the US can no longer be the mediator in peace talks with Israel.
The US president has sought to bring Israel and the Palestinians back to the negotiating table, with talks stalled since 2014.
Speaking Sunday evening 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".
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 delegates began meeting Monday morning, with talks expected to end in the evening with a joint statement.
The last meeting of the PCC in 2015 called for the ending of security coordination with Israel, but its decisions were non-binding and it was never implemented.