Iranian officials on Tuesday urged young people to form human chains to protect power plants, as Donald Trump warned that a “whole civilization will die tonight” if Tehran does not meet his latest deadline to agree to a deal that includes reopening the Strait of Hormuz.

While Iran cannot match the sophistication of U.S. and Israeli weaponry or their dominance in the air, its chokehold on the strait is roiling the world economy and raising the pressure on Trump both at home and abroad to find a way out of the standoff.

Officials involved in diplomatic efforts said talks were ongoing, but Iran has rejected the latest American proposal, and it was unclear if a deal would come in time to head off Trump’s threatened attacks. World leaders and experts warned that strikes as destructive as Trump threatened could constitute a war crime.