Rock samples from deep within Yucca Mountain, in Nevada, showed that the fault runs directly beneath the site where the US federal government planned to store 70,000 tonnes of highly radioactive waste.

More than $8bn (£4bn) has already been spent on the $58bn project, which had been due to open in 2017, but the proposals - approved by George Bush in 2002 - may now have to be redrawn.

Samples taken from 76 metres below the surface of the mountains, which are around 90 miles north-west of Las Vegas, revealed that the Bow Ridge fault passes hundreds of metres to the east of where scientists believed it lay.

The measurements were backed up by US Geological Survey maps and a letter, the Las Vegas Review-Journal reported yesterday.

The fault is now thought to run beneath a storage pad where spent radioactive fuel canisters would be cooled before being sealed in a maze of tunnels inside the mountain.

Bob Loux, the executive director of the Nevada Agency for Nuclear Projects, expressed amazement that the US Department of Energy had only just carried out the "11th hour" drilling tests.

"It certainly looks like DoE has encountered a surprise out there, and it certainly speaks to the fact they haven't done the technical work they should have done years ago," he told the paper.

"It's going to have to cause some change of the design in the final analysis. It's going to impact the safety case."

The state of Nevada - the third most seismically unstable in the US - has long opposed the project on the grounds that earthquake activity makes the site unsafe.

Since 1976, there have been 621 seismic events of magnitude greater than 2.5 on the Richter scale within a 50-mile radius of Yucca Mountain.

The Department of Energy refused to comment on the claims, but project officials said they were continuing to develop repository design, construction and operating plans in preparation for applying next year for a licence from the Nuclear Regulatory Commission.