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If Netanyahu fails to form a government, Israel is set on a path for its third election with its government in a deep-seated deadlock.
Blue and White and Likud are currently tied on seats after the country's second election in a year.
The European Union said any "settlement plan" would be considered "illegal" under international law after Israeli Prime Minister Benjamin Netanyahu announced he planned to annex parts of the occupied West Bank.
Watch: Netanyahu joins Johnson outside number 10 on surprise visit to London
There were no immediate reports of casualties, though the Israeli Defense Forces said a number of hits have been confirmed.