Demonstrating a significant shift in America’s nuclear strategy, the Bush administration intends to produce – not just research – a thermonuclear bunker-busting bomb to destroy hardened, deeply buried targets, the Pentagon has acknowledged for the first time.

The weapon – known as the Robust Nuclear Earth Penetrator – would be a full-power hydrogen bomb that would throw up enormous clouds of radioactive dust while wreaking large-scale damage and death if used in an urban area. It would be thousands of times more powerful than the conventional “bunker busters” dropped on Baghdad in an attempt to kill former Iraqi leader Saddam Hussein.