“Jerusalem is a final-status issue that must be resolved through direct negotiations between the two parties on the basis of the relevant Security Council and General Assembly resolutions, taking into account the legitimate concerns of both the Palestinian and the Israeli sides,” Mr. Guterres said.
“In this moment of great anxiety, I want to make it clear: there is no alternative to the two-state solution,” he said. “There is no Plan B.”
In Rome, Pope Francis prayed that Jerusalem’s status be preserved and needless conflict avoided.
“I cannot remain silent about my deep concern for the situation that has developed in recent days,” Francis said at his weekly general audience at the Vatican. “And at the same time, I wish to make a heartfelt appeal to ensure that everyone is committed to respecting the status quo of the city, in accordance with the relevant resolutions of the United Nations.”
“Jerusalem is a unique city,” he said, “sacred to Jews, Christians and Muslims, where the Holy Places for the respective religions are venerated, and it has a special vocation to peace.”
In especially strong language, the pope added, “I pray to the Lord that such identity be preserved and strengthened for the benefit of the Holy Land, the Middle East and the entire world, and that wisdom and prudence prevail, to avoid adding new elements of tension in a world already shaken and scarred by many cruel conflicts.”
The European Union’s top diplomat, Federica Mogherini, expressed concern about “the repercussions this may have on the prospect of peace.”
In a statement, she reiterated the bloc’s position that Jerusalem should be a future capital of two states, Israeli and Palestinian, and that embassies should not be moved there until the city’s final status was resolved. She cited a 1980 United Nations Security Council resolution that condemned Israel’s attempted annexation of East Jerusalem as a violation of international law.
She called on actors in the region “to show calm and restraint in order to prevent any escalation.”
Within a few hours of Mr. Trump’s speech, eight countries on the 15-member Security Council — including some of America’s closest allies — requested an emergency meeting to be held before the end of the week. Diplomats said it would most likely be scheduled for Friday.
Joakim Vaverka, political coordinator of Sweden’s United Nations mission, said in a statement that the delegations of Bolivia, Britain, Egypt, France, Italy, Senegal, Sweden and Uruguay had sought the meeting, including a briefing by Mr. Guterres, “in light of the statement today by the president of the United States regarding the status of Jerusalem.”
The warnings by the pope, the United Nations and the European Union spoke to a broad fear that Mr. Trump’s announcement would be the death knell for an already moribund peace process and that it would pull the plug on a two-state solution.
Critics of the announcement said the change in policy removed any pretense that the United States is a neutral broker for peace. Palestinians and other Arabs in the region already view the Trump administration as leaning toward Israel’s right-wing government. The change in American policy “destroys the peace process,” said the Palestinian prime minister, Rami Hamdallah.
Some of the United States’ closest allies expressed apprehension.
Prime Minister Theresa May of Britain called Mr. Trump’s decision “unhelpful in terms of prospects for peace in the region.”
President Emmanuel Macron of France, who was in Algeria on Wednesday meeting with the country’s president and other figures, said in a news conference that the decision by Mr. Trump was “regrettable” and that “France and Europe are committed to a two-state solution.” He called on all parties to refrain from violence.
Germany’s chancellor, Angela Merkel, said through a spokesman that her government “does not support this position, because the status of Jerusalem is to be resolved in the framework of a two-state solution.”
Prime Minister Paolo Gentiloni of Italy wrote on Twitter: “Jerusalem holy city, unique on earth. Its future will be defined within the framework of the peace process based on the two states, Israel and Palestine.”
In China, the Ministry of Foreign Affairs spokesman, Geng Shuang, expressed support for a Palestinian state with East Jerusalem as its capital and urged all parties to the conflict to proceed cautiously. “What we worry about is any potential flare-up of regional tensions,” he said. “The status of Jerusalem is a complicated and sensitive issue.”
Britain’s foreign minister, Boris Johnson, told reporters in Brussels, “Clearly this is a decision that makes it more important than ever that the long-awaited American proposals on the Middle East peace process are now brought forward.”
That process, led by Mr. Trump’s son-in-law, Jared Kushner, has seemingly failed to get off the ground.
Leaders in the region had already warned against the move. A statement from the royal palace of King Abdullah II of Jordan, whose kingdom is the custodian of Al Aqsa Mosque in Jerusalem, emphasized that the city was critical to “achieving peace and stability in the region and the world.”
In Turkey, President Recep Tayyip Erdogan was convening a summit meeting of the main Pan-Islamic body next week in Istanbul to discuss the American move and to show, as his spokesman Ibrahim Kalin told reporters in Ankara, “joint action among Islamic countries.”
Mr. Kalin called the expected change a “grave mistake,” adding that “Jerusalem is our honor, Jerusalem is our common cause, Jerusalem is our red line.”
Iran, unsurprisingly, condemned the change. Its supreme leader, Ayatollah Ali Khamenei, said at a conference in Tehran on Wednesday that it reflected the “incompetence and failure” of the American government.
Like much of Europe, the Vatican has long been sympathetic to the plight of Palestinians. The Vatican established full diplomatic relations with Israel in 1994, and Pope John Paul II and Pope Benedict XVI visited Israel and the Palestinian territories.
In 2012, the Vatican called for “an internationally guaranteed special statute” for Jerusalem, with the goal of “safeguarding the freedom of religion and of conscience, the identity and sacred character of Jerusalem as a Holy City, (and) respect for, and freedom of, access to its holy places.”
Francis visited the Holy Land in 2014, but he upset some Israelis by flying by helicopter directly from Jordan to the “State of Palestine,” as the Vatican schedule at the time referred to the territories. He visited Israel afterward.
In 2015, the Vatican entered into a treaty with the “State of Palestine.”
On Tuesday, Francis spoke by telephone to the Palestinian Authority president, Mahmoud Abbas, about the unfolding crisis. Before the pope’s public remarks to the faithful at the Vatican on Wednesday, he met privately with a group of Palestinians participating in interfaith dialogue with officials at the Vatican.
“The Holy Land is for us Christians the land par excellence of dialogue between God and mankind,” he said. “The primary condition of that dialogue is reciprocal respect and a commitment to strengthening that respect, for the sake of recognizing the rights of all people, wherever they happen to be.”