U.S. President Donald Trump on Tuesday warned of the potential “death of an entire civilization” in Iran if the country does not respond to his final ultimatum to accept U.S. demands to end the war.

Writing on his platform Truth Social, Trump said: “An entire civilization will die tonight, and will never return. I don’t want that, but it will probably happen. Who knows?”

Trump did not provide further details, but he has previously indicated that the U.S. military could target civilian infrastructure in Iran—including bridges and power plants—if no agreement is reached within the specified timeframe.

The remarks come amid escalating military tensions between the United States and Iran, raising global concerns over a widening conflict and its humanitarian and economic consequences.