President Nicolas Maduro of Venezuela also attended by special invitation of Mr. Erdogan.
A conservative Muslim, Mr. Erdogan has made the Palestinians’ fate a leading cause of his politics, styling himself as a leader of the wider Muslim community. He criticized some Arab states for what he called their weak response to Mr. Trump’s decision, suggesting they were intimidated by the United States.
Mr. Abbas on Wednesday told the gathering that Mr. Trump had committed the “greatest crime” with his declaration, and that the Palestinians would no longer accept any role of the United States in peace negotiations with Israel.
“Jerusalem is and always will be the capital of Palestine,” he said, adding that the United States was giving it away as if it were an American city. “It crosses all the red lines,” Mr. Abbas said.
Mr. Erdogan urged nations of the world to recognize the state of Palestine, and declared Jerusalem as its occupied capital. He warned there would be no peace in the region unless the city’s status was recognized as such.
The Turkish leader also voiced some of the strongest criticism of Mr. Trump. “How can you take a decision like that on your own?” Mr. Erdogan said, addressing Mr. Trump directly through a live news briefing.
Saying he expected the Americans to “reverse their mistake,” Mr. Erdogan added of Israel that “Palestine’s fate cannot be left in the hands of a country that brutally kills women and children alike.”
“Israel has been rewarded for all the terrorism that it did, and the award has been given by Trump, although he is alone,” Mr. Erdogan said. “While we were working for peace, we got the biggest slap in our face of our times.”
Calling Israel a terrorist state, he warned that “Israel will never have any legitimacy in Jerusalem.”