The Arab League held an emergency session on Tuesday evening after the Israeli prime minister announced the plan in a live press conference.
Netanyahu, who is fighting for his political life before elections on 17 September, said he would permanently seize up to a third of the West Bank, a move that for decades has been considered an endgame scenario for Palestinians’ aspirations of statehood.
“We haven’t had this kind of opportunity since the  six-day war, and may not have it again for another 50 years,” Netanyahu said, referring to the war in which Israel captured the land.
Arab foreign ministers meeting in Cairo condemned the plan as “a dangerous development and a new Israeli aggression by declaring the intention to violate the international law”.
“The league regards these statements as undermining the chances of any progress in the peace process and will torpedo all its foundations,” the ministers said.
Jordan’s foreign minister, Ayman Safadi, said Netanyahu’s plan was an outrageous election ploy and a “dangerous escalation that shatters the foundations of the peace process”.
Netanyahu made the announcement in front of a large map showing Israeli sovereignty extending over the vast majority of the Jordan Valley and slicing off the eastern border with Jordan.
“Killing all chances for peace for electoral purposes is irresponsible, dangerous,” Safadi added in a tweet.
Turkey’s foreign minister said the plan was racist and incendiary. “The election promise of Netanyahu, who is giving all kind of illegal, unlawful and aggressive messages before the election, is a racist apartheid state,” Mevlüt Çavuşoğlu wrote on Twitter.
“Will defend rights and interests of our Palestinian brothers & sisters till the end,” he added.
The president of the Palestinian Authority, Mahmoud Abbas, said he would pull out of any previous agreements signed with the Israeli government if it went ahead with the move – a threat he has previously made without following through.
“[We maintain] the right to defend our rights and achieve our goals through all available means regardless of the consequences,” Abbas said, according to a report by the state-run Wafa news agency.
Ayman Odeh, the leader of an alliance of Arab parties in Israel, called Netanyahu’s statement “not just election spin” but “a vision of apartheid”.
Netanyahu hinted on Tuesday night that the plan had the support of the White House. “I am waiting to do this in maximum coordination with [Donald] Trump,” he said in a speech broadcast live on Israeli television.
A White House official said there had been no change in US policy and would not comment further.
Late on Tuesday evening, Netanyahu was dragged away by his security team from a campaign rally in the southern city of Ashdod after air sirens sounded. The Israeli military said two rockets had been launched from Gaza, both of which were intercepted by its aerial defence system.
Despite the implications for a future two-state solution, Arab states would be under significant pressure not to escalate if the annexation went ahead, analysts said.
The fate of the Palestinians has diminished as a priority in many Arab capitals as the geopolitics of the region has shifted. Saudi Arabia and Israel share an interest in combating Iranian influence in the Middle East. Jordan and Egypt have long ago signed peace treaties with Israel, easing the flow of American aid and military equipment on which both depend.
Significant implications are likely to be felt across the border with the West Bank in Amman. “Jordan has real existential fears with any outcome other than a two-state solution,” said Osama al-Sharif, a Jordanian analyst and columnist.
Roughly 2 million Palestinians live in Jordan, most of them naturalised but barred from certain jobs on the basis they will one day be able to return to their own state. Jordanians living in the East Bank also fear that Israeli consolidation of its occupied territories could push new waves of refugees into Jordan, at a time when the country is already hosting an estimate 1.4 million Syrian refugees.
The international community considers Israeli settlements illegal under international law, built on land confiscated from Palestinian families. Extending Israeli sovereignty over such a large area would also be seen as putting an end to fading hopes for a Palestinian state, as there would be little unbroken land on which to create it.
Trump’s recognition of Jerusalem as Israel’s capital early in his term further damaged the two-state ideal. The Palestinians regard the occupied eastern section of Jerusalem as the capital of any future state, and cut contact with Washington after the declaration.
Earlier this year, Trump also recognised Israeli sovereignty over the Golan Heights, a plateau Israel captured from Syria in the same 1967 conflict and annexed in 1981. The move broke from the international consensus following the second world war that forbids territorial conquest during war.
In Israeli politics, annexation is a popular position. Israel has long stated it would want to keep the 2,400 sq km (927 sq mile) Jordan Valley to maintain control over the international border.