President Donald Trump's futuristic "Golden Dome" missile defence system will cost about $1.2 tn (£882bn) to develop, deploy and operate over two decades, a new report from the nonpartisan Congressional Budget Office estimates.
That figure is significantly higher than the initial sum of $175bn (£129.25bn) that had been earmarked.
Acquisition costs alone would be over $1tn, including for the interceptor layers and a space-based missile warning and tracking system, the watchdog said in a report published on Tuesday.
The "Golden Dome", which aims to encompass the US, is designed to counter aerial threats to the US, including ballistic and cruise missiles.
Just days after returning to the White House in January, Trump unveiled his plans for the system, aimed at countering "next-generation" aerial threats.
