"Under international law, deliberately attacking civilians and civilian infrastructure is a war crime," UN high commissioner for human rights Volker Turk said in a statement, insisting that "anyone responsible for international crimes must be held to account by a competent court."

His comment came as US President Donald Trump ramped up his rhetoric against Iran, vowing to carry out the "complete demolition" of critical infrastructure, particularly bridges and power plants if Iran did not agree a deal by late Tuesday.

Hours before the deadline, the Israeli military said it had already completed a broad wave of strikes targeting "infrastructure sites" across Iran.

Writing on Truth Social, Trump stated that "a whole civilisation will die tonight, never to be brought back again. I don't want that to happen, but it probably will", if the country does not heed his call for a deal.

Turk did not explicitly mention Trump nor the other countries involved in the conflict that began on February 28. But he said "I deplore the tirade of incendiary rhetoric being used in the Middle East war over the last couple of weeks by all parties."

In particular, he highlighted "the latest threats to annihilate a whole civilisation and to target civilian infrastructure".

"This is sickening," he said, warning that "carrying through on such threats amounts to the most serious international crimes".

The UN rights chief stressed that "threats that spread fear and terror among civilians are unacceptable and must cease immediately".

He called on the international community to "take urgent steps to de-escalate the situation and to help protect the lives of all civilians".