Together with Mr. Tillerson, the main diplomat of the European Union, Federica Mogherini, made it clear that Europe saw the president's announcement as a threat to peace in the Middle East.
"We believe that any action that undermines these efforts should be absolutely avoided," he said. "A path must be found through negotiations to resolve the state of Jerusalem as the future capital of both states."
Just a few hours before Trump was expected to declare that Jerusalem was the capital of Israel, Mr. Tillerson said that peace in the Middle East was still possible.
Mr. Tillerson, during a press conference at NATO headquarters in the heart of Europe, said he did not want to get ahead of the president's official announcement, but expressed assurances about the expected consequences of the decision.
"The president is very committed to the Middle East peace process," Tillerson said.
Mr. Tillerson has been largely excluded from the usual round trip between Israelis and Palestinians that many secretaries of state spent much of their driving duties. Instead, Mr. Trump entrusted that task to his son-in-law and principal advisor, Jared Kushner.
At least one former official of the Obama administration also intervened with harsh criticism. John O. Brennan, former director of the Central Intelligence Agency, said in a statement that Mr. Trump's action was "reckless" and that "it would harm US interests in the Middle East over the next few years and the region will return. more volatile. "
Administration officials said they expected the withdrawal of Palestinians and others, but said the measure would accelerate, not hinder, the peace process.
Mr. Trump promised to move the embassy during the 2016 presidential campaign, a position that attracted pro-Israeli American evangelical and Jewish voters, including Sheldon Adelson, the casino mogul of Las Vegas. In fulfilling that promise, Mr. Trump's aides said he was improving his credibility as a peacemaker.
The announcement, the officials said, was the recognition of the current and historical reality. West Jerusalem is the seat of the government of Israel, and recognizing it as such would eliminate the ambiguity of the American position, they said.
The process of transferring the embassy to Jerusalem will take several years, they said. As a result, the president plans to sign a national security exemption that allows the administration to keep it in Tel Aviv for an additional six months.
Jerusalem is one of the most fiercely contested real estate estates in the world, with each of the parties contesting each other's claims. The Palestinians see East Jerusalem as the capital of a future Palestinian state, and most of the world considers it occupied territory. The Old City of Jerusalem has the third holiest mosque in Islam and the holiest site in Judaism, which makes the state of the city a sensitive issue for Muslims and Jews alike.
Mr. Trump, these officials said, would make it clear that the United States was not taking a stand on whether, or how, Jerusalem would be divided between Israel and the Palestinians. Nor will it take a position in a disputed area of the Old City, known as the Temple Mount for Jews and the Noble Sanctuary for Muslims, which has been a flashpoint for tensions.
Mr. Kushner and Jason D. Greenblatt, the president's special envoy, have been working for months to prepare for a negotiation between Israelis and Palestinians. Although they have little to publicly show in the effort, they say they have progressed behind the scenes.
These efforts, according to experts from the Middle East, will be compromised by the announcement on Wednesday. But Mr. Kushner and Mr. Greenblatt, the president's special envoy, supported the president's decision, authorities said.
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