Donald Trump's rhetoric is becoming more violent, as he issues a grave threat toward Iran.

The US President says 'a whole civilisation will die tonight' unless the Strait of Hormuz reopens, warning US forces will demolish Iranian bridges and power . 

But Tehran is holding steadfast. 

The Guardian's defence and security editor Dan Sabbagh told Ryan Bridge Iranian infrastructure's already being bombed. 

He says Israel's blown up eight bridges across Tehran's rail network. 

US forces also bombed targets on Kharg Island overnight - which exports most of Iran's oil. 

Meanwhile, Foreign Minister Winston Peters is in Washington, where he's wrapped up a meeting with US Secretary of State Marco Rubio.