Netanyahu's controversial pledge involves extending Israel's sovereignty over the Jordan Valley and the northern Dead Sea which account for one-third of the West Bank if he wins next week's elections. It would not include however annexing any Palestinian cities such as Jericho.
The pre-election promise late Tuesday drew immediate condemnation from Arab powerhouses with many warning of disastrous consequences for the stagnant Israeli-Palestinian peace process.
"The announcement constitutes a dangerous development and a new Israeli aggression," Arab foreign ministers said after an Arab League meeting in Cairo.
They also warned in a statement of "the ramifications of these dangerous, illegal and irresponsible" moves saying it would "undermine the chances of progress in the peace process".
Jordanian and Palestinian officials said any such measure risks "killing off" and "destroying" the entire peace process, which has failed to make any progress for years.
Damascus "strongly condemned" Netanyahu's vow, with a Syrian foreign ministry source telling the state news agency SANA that it was an "expansionist" plan which would be a "flagrant violation" of international treaties.
Israel occupied the West Bank in the 1967 Six-Day War in a move never recognised by the international community.
It also seized -- and later annexed -- part of the Golan Heights from Syria, and the two countries remain technically at war.
Saudi Arabia flagged the announcement as a "dangerous escalation", calling for an "emergency meeting" of the foreign ministers of the 57 member states of the Organisation of Islamic Cooperation (OIC).
Beyond the Arab world, Turkey slammed Netanyahu pledge as "racist".
It would "defend (the) rights and interests of our Palestinian brothers and sisters till the end," said Turkish Foreign Minister Mevlut Cavusoglu.
The United Nations remonstrated that Netanyahu's plan would have no "international legal effect."
Meanwhile, the European Union said the pledge undermines any prospects for peace.
"The policy of settlement construction and expansion... is illegal under international law and its continuation, and actions taken in this context, undermine the viability of the two-state solution and the prospects for a lasting peace," an EU spokesperson said in a statement.
When announcing his pledge, Israeli prime minister said he would take the step in coordination with his ally, US President Donald Trump.
But by Wednesday morning there had still been no official US reaction to Netanyahu's latest statements.
Israel has enjoyed a strong US support under the Trump administration which in a highly controversial move overturned decades of US policy to recognise the holy city of Jerusalem as the capital of the Jewish state in 2017.
Earlier in 2019, Trump also declared Israeli sovereignty over the Golan Heights, which Israel seized Syria in the 1967 Six-Day War, along with the West Bank and east Jerusalem.
More than 600,000 Israeli Jewish settlers now live in the West Bank and annexed east Jerusalem, among three million Palestinians.
Arab and Muslim leaders have unanimously decried the US moves backing Netanyahu's policies, but done little to challenge them.
They have instead insisted on achieving a two-state solution and establishing a Palestinian state based on the borders of 1967 with East Jerusalem as its capital.
Trump's son-in-law Jared Kushner has been tasked with hammering out a peace plan to resolve the bitter Israeli-Palestinian conflict.
The plan's economic aspects were unveiled at a Bahrain conference in June, floating the prospect of pumping some $50 billion worth of investment into a stagnant Palestinian economy.
It failed however to address key Palestinian demands such as the establishment of their own independent state. It remains unclear when Kushner's full plan will be rolled out with the Israeli elections looming on September 17.