BEIRUT— With President Donald Trump poised to do what no other president has been willing to do — move the U.S. Embassy in Israel to Jerusalem — leaders and analysts in the region warned Tuesday that it could spur insecurity and instability in a part of the world already beset by both.

Fulfilling a campaign pledge, Trump will declare Jerusalem the capital of Israel in a speech at the White House on Wednesday, three senior administration officials said. At the same time, he will set in motion a multiyear process for moving the embassy from Tel Aviv to Jerusalem, the officials said.

The president laid the groundwork in a series of phone calls Tuesday to Saudi Arabia’s King Salman, Jordan’s King Abdullah II, Palestinian Authority President Mahmoud Abbas and Egyptian President Abdel-Fattah el-Sissi.

All the leaders issued strongly worded declarations opposing the idea, which they fear could stir violent passions in a city that has long been a nationalist and religious tinderbox.

Jerusalem was a divided city until 1967, when Israel captured the eastern half of the city in a war with its Arab neighbors. Palestinians have never accepted Israeli rule over the entire city and have insisted that east Jerusalem become the capital of any future Palestinian state, making decisions about its status especially fraught.

Even before the president unveiled his plan, the emerging outline was enough to send a sense of anger and apprehension coursing through the Arab world and beyond.

European allies appealed anew for moderation on such a sensitive matter, and United Nations Secretary-General Antonio Guterres said through a spokesman that the city’s status had always been regarded by the world body as a question that “must be resolved through direct negotiations.”

In Israel, security forces braced for a potential eruption of unrest, according to Israeli news reports. The government of Prime Minister Benjamin Netanyahu stayed largely silent in the run-up to Trump’s speech, seemingly worried that any display of satisfaction over an explicit American endorsement of its long-held position might generate even more of a backlash from Arab neighbors.

“Trump’s expected declaration on Jerusalem could turn into a match that would ignite a major fire in the violent region we are living in,” veteran Israeli commentator Shimon Shiffer wrote in the Yediot Aharonot newspaper this week.

The eve of the president’s statement saw the strongest public warning yet from Saudi Arabia, a key U.S. ally.

King Salman declared that any unilateral U.S. declaration on the status of Jerusalem would be a “dangerous step” and a “flagrant provocation of Muslims all over the world,” according to a statement carried by the official Saudi Press Agency.

Trump’s posture on Jerusalem drew expressions of bewilderment from some longtime watchers of the region, who pointed to a plethora of pitfalls awaiting.

“I’m just baffled,” said Thomas Lippman, an expert in Arab affairs and U.S.-Saudi relations at the Middle East Institute in Washington. “You don’t win the battle for Muslim hearts and minds by being seen as soft on Israel.”

The U.S. Embassy won’t be moved immediately, the officials said. In the meantime, Trump will sign a waiver to the 1995 law that demanded the State Department move the embassy by May 31, 1999.

Trump will not set a timetable, but one senior U.S. official said that opening a new U.S. embassy in another country routinely takes three to four years.

“We don’t just put a plaque on the door and open a mission,” the official said.

Palestinians have long considered Trump to be too partial toward Israel to be a fair broker in any peace process, and the latest developments brought new expressions of angst. A spokesman for Abbas, Nabil Abu Rudaineh, was quoted by the official Palestinian news agency WAFA as saying Abbas told Trump during their phone call that moving the embassy would have highly negative repercussions.

More than any other issue associated with the conflict, the status of Jerusalem is a consistent flashpoint. A disputed holy site in its walled Old City — known to Jews as the Temple Mount and Muslims as the Noble Sanctuary — has been at the heart of many outbreaks of violence, including tension that boiled over into deadly clashes this year.

Palestinians have threatened to cut off contacts with Washington if Trump makes unilateral decisions about Jerusalem’s status. The U.S. Consulate in Jerusalem, citing widespread calls by Palestinians for demonstrations in coming days, forbade U.S. government workers and their families from making personal trips to the Old City or the West Bank. It also advised U.S. citizens to exercise caution.

alexandra.zavis@latimes.com