As Arab and European nations call on Israel to stop its annexation plans, US President Donald Trump has declined to criticise the move.
The United Nations and European and Arab powers have warned Israel that its plans to annex Palestinian land would deal a major blow to peace.
With a majority of world powers urging Israel against annexation, the United States remained steadfast with its support.
One week before Israeli Prime Minister Benjamin Netanyahu is expected to start the annexation process, a UN Security Council session on Wednesday provided a final opportunity for the international community to urge him to change course.
"I call on the Israeli government to abandon its annexation plans," UN Secretary General Antonio Guterres told the virtual conference.
'Israeli annexation could ignite a religious war'
The UN coordinator for the Middle East, Nickolay Mladenov, said annexation "could irrevocably alter the nature of Israeli-Palestinian relations".
"It risks upending more than a quarter of a century of international efforts in support of a future viable Palestinian state living in peace, security and mutual recognition with the State of Israel," he said.
Seven European nations –– Belgium, Britain, Estonia, France, Germany, Ireland and Norway –– in a joint statement warned that annexation would "severely undermine" prospects for resuming the Middle East peace process.
"Under international law, annexation would have consequences for our close relationship with Israel and would not be recognised by us," they warned.
The head of the Arab League warned Israel’s annexation would inflame tensions and endanger peace in the Middle East, and could ignite “a religious war in and beyond our region.”
Arab League secretary general Ahmed Aboul Gheit said annexation "will destroy any prospect for peace in the future" and threaten regional stability.
US defers to Netanyahu
But the administration of President Donald Trump, a close ally of Netanyahu, has declined to criticise annexation and has rejected the consensus of most of the world that Israeli settlements on Palestinian land are illegal.
"Decisions about Israelis extending sovereignty to those places are decisions for the Israelis to make," Secretary of State Mike Pompeo told reporters in Washington.
Annexation of West Bank
Trump in January unveiled a Middle East plan that would pave the way for Israel to annex areas around Jewish settlements and the Jordan Valley that it captured in the 1967 Six-Day War.
The US plan envisions leaving about one-third of the West Bank, which Israel captured in 1967, under permanent Israeli control, while granting the Palestinians expanded autonomy in the remainder of the territory. The Palestinian capital would be on the outskirts of hotly contested Jerusalem.
An agricultural plain with precious water resources, the Jordan Valley makes up nearly a third of the occupied West Bank.
Israel's plan to annex Jordan Valley exclude Palestinian population hubs such as the city of Jericho, which risks becoming an enclave surrounded by Israeli territory under the plan.
The Palestinians, who seek all of the West Bank as part of an independent state, have rejected the plan, saying it overwhelmingly favours Israel.
The plan also calls for major economic investment into Palestinian areas, funded largely by Gulf Arab states that find common cause with Netanyahu and Trump in hostility toward Iran.
But US allies, including the United Arab Emirates and Jordan, one of two Arab states to have a peace treaty with Israel, have warned that annexation would jeopardise the Jewish state's hopes for better ties.
Pompeo brushed aside such concerns, saying the UN was "talking to all of the countries in the region" about the weeks ahead.
"I regret only that the Palestinian Authority has refused to participate in that," Pompeo said.
Palestinians urge action
At the UN, Palestinian representative Riyad al Malki said annexation would be a "crime".
"Israel seems determined to ignore that big red stop sign the international community erected to save lives," he said.
He warned that the Palestinians could approach the International Court of Justice and urged nations to impose sanctions on Israel if it goes ahead.
European nations, while opposed to annexation, have been split on how severely to respond if Israel goes ahead.
Israel's UN ambassador Danny Danon criticised the Palestinians, saying the stalemate was due to their refusal to negotiate.
"Some in the international community choose to reward the Palestinians' rejectionism and ignore reality," he said.
"Instead of confronting the Palestinian leadership, they have tried to appease them by buying every rotten bill of goods the Palestinians were selling."
Netanyahu can begin to consider annexation on July 1 under a coalition deal with his centrist rival turned partner Benny Gantz, who has been more cautious, especially in assessing reaction in the US.
Joe Biden, the presumptive Democratic nominee for president who leads Trump in polls, has voiced opposition to annexation.