The Organization of Islamic Cooperation on Monday called for a summit of Muslim nations if the United States takes the controversial decision to recognize Jerusalem as Israel's capital.
US President Donald Trump faces a key decision this week over Jerusalem's status, potentially breaking away from years of US policy and prompting a furious response from the Palestinians and the Arab world.
The Palestinian Authority has formally notified the US government of its opposition to any plan to move the US embassy to Jerusalem or recognize the city as the Israeli capital.
The 57-member OIC sought to amplify concern over the possible move in an emergency meeting on Monday in the Saudi Red Sea city of Jeddah.
"If the United States takes the step of recognizing Jerusalem as the so-called capital of Israel, we unanimously recommend holding a meeting at the level of council of foreign ministers followed by an Islamic summit as soon as possible," the pan-Islamic body said in a statement.
The OIC also warned that recognizing Jerusalem or establishing any diplomatic mission in the city would be seen as a "blatant attack on the Arab and Islamic nations."
The status of Jerusalem is one of the most contentious issues of the decades-long Israeli-Palestinian conflict.
Most of the international community, including the United States, does not formally recognize Jerusalem as Israel's capital, insisting the issue can only be resolved through final-status negotiations.
Central to the issue of recognition is the question of whether Trump decides to move the US embassy in Israel to Jerusalem.
All foreign embassies are located in Tel Aviv with consular representation in Jerusalem.
Israelis and Palestinians are eagerly watching to see whether he again renews a waiver delaying the move, as his predecessors have done.
There are suggestions that Trump will sign the waiver and decline to move the embassy for now, but later this week declare Jerusalem as Israel's capital.
Ziad Abu Amr, the deputy Palestinian prime minister, officially informed US Consul General Donald Blome on Monday of their opposition.
Palestinian President Mahmud Abbas has been speaking to foreign leaders to lobby against such a recognition.
Abu Amr "informed the US Consul General Donald Blome that moving the American embassy to Jerusalem or the US administration recognizing Jerusalem as the capital of Israel is unacceptable," a statement said, after a meeting in Ramallah.
It said any such move would be "disrespectful" and "contrary to the role of the US administration as a mediator and sponsor of the peace process."
The statement said doing so "disqualifies it from this role, and closes every door to continuing a serious peace process."
Israel, which seized the largely Arab eastern sector of Jerusalem during the 1967 Six-Day War and later annexed it, claims both halves of the city as its "eternal and undivided capital."
But the Palestinians want the eastern sector as capital of their promised state and fiercely oppose any Israeli attempt to extend sovereignty there.
Several peace plans have come unstuck over debates on whether, and how, to divide sovereignty or oversee the city's sites holy to Christians, Jews and Muslims.