Global concern mounted Wednesday ahead of an announcement by US President Donald Trump to recognize Jerusalem as Israel's capital, with Pope Francis joining a list of leaders warning of a potential dangerous fallout.
The move by Trump, set to come in a speech later Wednesday, would upend decades of careful US policy and ignore dire warnings of a historic misstep that could trigger a surge of violence in the Middle East.
A senior administration official said Trump would make the announcement at 1800 GMT from the White House on the city whose status is a critical issue in the Israeli-Palestinian conflict.
"He will say that the United States government recognises that Jerusalem is the capital of Israel," a senior administration official said on condition of anonymity.
"He views this as a recognition of reality, both historic reality and modern reality."
Plunging further into a decades-long dispute over a city considered holy by Jews, Muslims and Christians, Trump will also order planning to move the US embassy from Tel Aviv to Jerusalem.
Such planning would take years to implement, the official said.
- Frantic calls -
In a frantic series of calls, the leaders of Saudi Arabia, Egypt, Jordan, the European Union, France, Germany and Turkey all warned Trump against the move.
Anticipating protests, US government officials and their families were ordered to avoid Jerusalem's Old City and the West Bank, though the situation remained largely calm Wednesday.
Hundreds of Palestinians burned US and Israeli flags as well as pictures of Trump in the Gaza Strip, while relatively small clashes erupted near the flashpoint West Bank city of Hebron.
A range of world leaders issued further warnings.
"I cannot silence my deep concern over the situation that has emerged in recent days," Pope Francis said, a day after speaking by phone with Palestinian president Mahmud Abbas.
The pontiff added that maintaining Jerusalem's status quo was important "in order to avoid adding new elements of tension to an already volatile world that is wracked by so many cruel conflicts".
British foreign minister Boris Johnson, speaking as he arrived for a NATO meeting in Brussels, expressed concern "because we think that Jerusalem obviously should be part of the final settlement between the Israelis and the Palestinians, a negotiated settlement".
British Prime Minister Theresa May said she planned to call Trump about his plan.
China warned it could fuel tensions in the region and Iranian President Hassan Rouhani said "Muslims must stand united against this major plot."
Turkish President Recep Tayyip Erdogan called for a summit of the Organisation of Islamic Cooperation (OIC), the main pan-Islamic body, in Istanbul on December 13 "to display joint action among Islamic countries" over Jerusalem.
"Such a step will only play into the hands of terror groups," Erdogan said at a joint news conference in Ankara after talks with Jordan's King Abdullah II.
Jordan and the Palestinians also called for an emergency meeting of the Arab League in Cairo.
But in a surprise move, Israeli Prime Minister Benjamin Netanyahu refrained from commenting on the issue on Wednesday in his first speech since Trump's plan was confirmed.
- Trump 'committed' to peace -
US Secretary of State Rex Tillerson defended Trump's approach in Brussels, saying the president was "very committed" to the Middle East peace process.
Trump's move comes close to fulfilling a campaign promise, and will delight his political donors and the conservative and evangelical base so vital for the embattled president.
Most of the international community does not formally recognise Jerusalem as Israel's capital, insisting the issue can only be resolved in negotiations.
The White House argues the move would not prejudge final talks and would represent the reality that west Jerusalem is and will continue to be part of Israel under any settlement.
Trump "is prepared to support a two-state solution... if agreed to by the two parties," a second US official said.
Critics say Trump's approach could extinguish his own efforts to broker Middle East peace while igniting the flames of conflict in a region already reeling from crises in Lebanon, Syria, Iraq, Yemen and Qatar.
- Three days of protest -
The Palestinian armed Islamist movement Hamas has threatened to launch a new "intifada" or uprising.
Palestinians called for three days of protests -- or "days of rage" -- starting Wednesday, raising fears of potential unrest.
Israel seized the largely Arab eastern sector of Jerusalem during the 1967 Six-Day War and later annexed it, claiming both sides of the city as its capital.
The Palestinians want the eastern sector as the capital of their future state.
Trump was pushed to act on the embassy as a result of the a 1995 law, which stated that the city "should be recognised as the capital of the state of Israel" and the US embassy be moved there.
A waiver has been invoked by successive US presidents, postponing the move on grounds of "national security" once every six months, meaning the law has never taken effect.
Several peace plans have unravelled in the past decades over the issue of how to divide sovereignty or oversee holy sites in Jerusalem.