Muslim leaders have condemned US President Donald Trump's recognition of Jerusalem as the capital of Israel.
They called on the world to respond by recognising East Jerusalem as the capital of Palestine.
Turkish President Recep Tayyip Erdogan, who hosted the summit of more than 50 Muslim countries in Istanbul, said the US move meant that Washington had surrendered its role as broker in efforts to end the Israeli-Palestinian conflict.
"From now on, it is out of the question for a biased United States to be a mediator between Israel and Palestine, that period is over," Mr Erdogan said at the end of the meeting of the Organisation of Islamic Cooperation member states.
"We need to discuss who will be a mediator from now on. This needs to be tackled in the United Nations too," Mr Erdogan said.
A communiqué posted on the Turkish Foreign Ministry website said the emirs, presidents and ministers gathered in Istanbul regarded President Trump's move "as an announcement of the US administration's withdrawal from its role as sponsor of peace".
It described the decision as "a deliberate undermining of all peace efforts, an impetus for extremism and terrorism and a threat to international peace and security".
Leaders including Palestinian President Mahmoud Abbas, Iran's President Hassan Rouhani and Jordan's King Abdullah, a close US ally, all criticised Washington's move.
"Jerusalem is and always will be the capital of Palestine," Mr Abbas said, adding that President Trump's decision was "the greatest crime" and a violation of international law.
The Trump administration has said it remains committed to reaching peace between Israel and the Palestinians and its decision does not affect Jerusalem's future borders or status.
It says any credible future peace deal will place the Israeli capital in Jerusalem and ditching old policies is needed to revive a peace process frozen since 2014.
Israeli Prime Minister Benjamin Netanyahu has said he is "not impressed" by the Muslim leaders' statements on Jerusalem.
He said he believed many countries would follow President Trump's lead and recognise Jerusalem as Israel's capital.
"The Palestinians would do better by recognising reality and acting in favour of peace and not extremism," Mr Netanyahu said.
"They should recognise another fact concerning Jerusalem: It is not only the capital of Israel, but we also maintain respect in Jerusalem for the freedom of worship for all religions, and we are the ones in the Middle East who do this like no-one else."
