A general view picture shows the Israeli settlement of Efrat in the Gush Etzion settlement in the Israeli-occupied West Bank. Reuters

Expanding Israeli settlements in the occupied Palestinian territories constitutes "a war crime" and risks eliminating any likelihood of a viable Palestinian state, the UN rights chief warned on Friday.

Volker Turk said there had been a drastic acceleration in Israeli illegal settlement building in the occupied West Bank as it wages a relentless war in the Palestinian territory of Gaza.

The UN high commissioner for human rights said creating and expanding settlements amounted to the transfer by Israel of its own civilian population into occupied territories.

"Such transfers amount to a war crime that may engage the individual criminal responsibility of those involved," Turk said in a report to the UN Human Rights Council.

Reported Israeli plans to build another 3,476 settler homes in the West Bank colonies of Maale Adumim, Efrat and Kedar "fly in the face of international law", he said.

Spain echoed the sentiment on Friday, with its foreign ministry saying it "strongly condemns" the planned settlements that "undermine efforts to achieve a two-state solution and are an obstacle to peace".

UN High Commissioner for Human Rights Volker Turk speaks at the European headquarters in Geneva. File/AP

France's foreign ministry also said it "strongly condemns" the settlement plan and called on the Israeli government to "immediately reverse this decision".

Israel seized the West Bank, east Jerusalem and the Gaza Strip in the 1967 Arab-Israeli war.

It is illegal under international law for Israel to establish settlements in those Palestinian territories.

Despite opposition abroad, Israel has built dozens of settlements across the West Bank in recent decades.

They are home to more than 490,000 Israelis, living in the same territory as around three million Palestinians.

Israel gave the go-ahead for the new homes less than two weeks after US Secretary of State Antony Blinken said any settlement expansion would be "counterproductive to reaching enduring peace" with the Palestinians.

Agence France-Presse