The first new bomber in 30 years could cost nearly $700m (£569m) each and can carry nuclear and conventional weapons.

As expected, specific details of the aircraft remain shrouded in secrecy.

But US Defence Secretary Lloyd Austin said it was "a testament to America's enduring advantages in ingenuity and innovation".

The B-21 Raider was unveiled during a ceremony on Friday at manufacturer Northrop Grumman's facility in California.

Mr Austin said the plane would offer significant advances over existing bombers in the US fleet, stating that "even the most sophisticated air defence systems will struggle to detect the B-21 in the sky".

"Fifty years of advances in low-observable technology have gone into this aircraft," he said.

He added that the plane was also built with an "open system architecture," which allows for the incorporation of "new weapons that haven't even been invented yet".

While the potential for an uncrewed flight was not mentioned during the ceremony, a US Air Force spokeswoman said the aircraft was "provisioned for the possibility, but there has been no decision to fly without a crew".

The first flight by a B-21 is expected to take place next year.

It will eventually replace the B-1 and B-2 models and the fleet is estimated to cost $203bn (£165bn) to develop, buy and operate over 30 years, according to Bloomberg.

Six planes are currently in production, the manufacturer said, adding they would feature the "next generation of stealth" and that it is employing unspecified "new manufacturing techniques and materials".

The US Air Force is planning to acquire at least 100 of the aircraft.