WASHINGTON/JERUSALEM (REUTERS) - US President Donald Trump on Wednesday (Dec 6) will recognise Jerusalem as Israel's capital and set in motion the relocation of the US Embassy to the ancient city, senior US officials said, a decision that upends decades of US policy and risks fueling violence in the Middle East.

Facing an outcry of opposition from Arab capitals, Trump, in a landmark speech, will announce he has ordered the State Department to begin developing a plan to move the embassy from Tel Aviv in what is expected to be a process that takes three to four years, the officials said.

He will not set a timetable for the move. Trump will sign a national security waiver that authorises him to delay the embassy relocation for now, since the US diplomats do not yet have a building in Jerusalem to move into, security arrangements or housing for diplomats, the officials said.

Still, Trump's endorsement of Israel's claim to all of Jerusalem as its capital would reverse long-standing US policy that the city's status must be decided in negotiations with the Palestinians, who want East Jerusalem as the capital of their future state.

The international community does not recognise Israeli sovereignty over the entire city, home to sites holy to the Muslim, Jewish and Christian religions.

The officials, who briefed reporters ahead of Trump's speech at 1 pm EST (1800 GMT) on Wednesday, insisted that Trump's decision, intended to fulfill a key campaign promise, was not meant to pre-judge the outcome of eventual talks on the final status of Jerusalem or other major disputes between the two sides.

Instead, one of the officials contended that Trump's announcements reflected the "historic reality" of Jerusalem as the centre of Jewish faith and the "modern reality" that it is the seat of Israeli government. Such arguments are not likely to sway the Palestinians and the broader Arab world.

Palestinian President Mahmoud Abbas, Jordan's King Abdullah, Egyptian President Abdel Fattah al-Sisi and Saudi Arabia's King Salman joined a mounting chorus of voices warning that unilateral US steps on Jerusalem would derail a fledgling US-led peace effort and unleash turmoil in the region after they received phone calls from Trump on Tuesday (Dec 5) informing them that he intends to move the US embassy in Israel to Jerusalem.

The White House said that Trump had also spoken with Israeli Prime Minister Benjamin Netanyahu, a longtime proponent of a US embassy move to Jerusalem. Netanyahu's office did not respond to a request for comment, but a senior Israeli minister welcomed Trump's decision while vowing that Israel would be prepared for any outbreak of violence.

White House spokesman Sarah Sanders said that Trump, who promised during the presidential campaign to move the embassy in Israel, would give a speech on Wednesday about his Jerusalem decision.

"The president I would say is pretty solid in his thinking at this point," she said, declining to provide details.

Trump notified Abbas "of his intention to move the American Embassy from Tel Aviv to Jerusalem", Abbas spokesman Nabil Abu Rdainah said.

Abbas, in response, "warned of the dangerous consequences such a decision would have to the peace process and to the peace, security and stability of the region and of the world" and also appealed to the Pope and the leaders of Russia, France and Jordan to intervene.

The Jordanian monarch, whose dynasty is the custodian of the Muslim holy sites in Jerusalem, told Trump that moving the embassy would have "dangerous repercussions" for the region and would obstruct US efforts to promote Israeli-Palestinian peace talks, according to a palace statement.

King Salman stressed to Trump that any US announcement on the status of Jerusalem would "inflame Muslim feelings all over the world", the Saudi Press Agency said.

None of the leaders' statements said whether Trump, who was also due to talk to Israeli Prime Minister Benjamin Netanyahu, specified the timing of an embassy move, a notion supported by successive governments in Israel, a close US ally.

But US officials, speaking on condition of anonymity, said Trump was expected to sign a national security waiver - as have his predecessors - keeping the embassy in Tel Aviv for another six months but would commit to expediting a move. It was unclear, however, whether he would set a date.

The Trump administration would need time to overcome logistical issues such as lack of a secure embassy building and staff housing in Jerusalem, according to one US official.

Trump appears intent on satisfying the pro-Israel, right-wing base that helped him win the presidency but which was disappointed when he delayed the embassy move in June.

Israel captured Arab East Jerusalem in the 1967 Middle East war and later annexed it, a move not recognised internationally.

'A BIG MISTAKE'

Israeli Intelligence Minister Israel Katz, who met last week with US officials in Washington, told Israel's Army Radio: "My impression is that the president will recognise Jerusalem, the eternal capital of the Jewish people for 3,000 years, as the capital of the state of Israel."

Asked whether Israel was preparing for a wave of violence if Trump recognises Jerusalem as the Israeli capital, he said: "We are preparing for every option. Anything like that can always erupt. If Abu Mazen (Palestinian President Mahmoud Abbas) will lead it in that direction then he will be making a big mistake."

Islamist militant groups such as Al-Qaeda, Hamas and Hezbollah have in the past tried to exploit Muslim sensitivities over Jerusalem to stoke anti-Israel and anti-US sentiment.

Asked whether Trump recognised that his Jerusalem decision could spark violence, Sanders said: "A number of things have been looked at that have been weighed into the president's decision."

Senior US officials told Reuters some officers in the State Department were also deeply concerned and the European Union, the Palestinian Authority, Saudi Arabia and the Arab League all warned that any such declaration would have repercussions across the region.

Turkey threatened on Tuesday to cut diplomatic ties with Israel if Trump recognises Jerusalem.

Netanyahu has so far declined to speculate on what Trump might say.

But Katz took to Twitter to reject Turkey's threat and reiterate Israel's position on the city, which is one of a long list of stumbling blocks in years of failed peace talks with the Palestinians.

"We don't take orders or accept threats from the president of Turkey," he wrote.

A US official said the consensus US intelligence estimate on US recognition of Jerusalem as Israel's capital was that it would risk triggering a backlash against Israel, and also potentially against US interests in the Middle East.

It is also likely to upset an Israeli-Palestinian peace push led by Trump's son-in-law and senior adviser Jared Kushner in pursuit of what the US president has called the "ultimate deal". The initiative has made little progress.

Arab criticism of Trump's plan contrasted sharply with the praise Washington's traditional Arab allies heaped on him at the beginning of his administration. They saw Trump as re-engaging in the region after what they perceived as former President Barack Obama's distancing of himself from them, as well as taking a tougher stand against Iran than Obama.

The European Union's top diplomat Federica Mogherini said on Tuesday that "any action that would undermine" peace efforts to create two separate states for the Israelis and the Palestinians "must absolutely be avoided."

UN Secretary-General Antonio Guterres has "consistently warned against any unilateral action that would have the potential to undermine the two-state solution," UN spokesman Stephane Dujarric told reporters in New York.

The Arab League and Saudi Arabia repeated past warnings, following statements by France and Jordan in recent days.

Past Israeli-Palestinian rifts have deteriorated into protests, attacks and fighting and further destabilised the region.