LONDON — Construction workers drilled a hole through a 6,000-year-old platform near Britain's iconic Stonehenge, causing irreparable damage to the ancient structure, archaeologists said on Thursday.

The structure in Blick Mead was drilled by Highways England workers as part of preparations for a four-lane highway tunnel to run beneath Stonehenge, said David Jacques, the lead archaeologist at the site.

"It’s complete vandalism," he said. "We have dug in the area since 2005, carefully sieving and working at times with toothbrushes. And for them to have come in and done things with a hand drill and just smashed through the surface is really upsetting and appalling."

Blick Mead, which is about a mile from Stonehenge, was unique in Western Europe and could have been crucial to understanding why Stonehenge was built where it was, he added.

Of particular significance were a series of remarkably well-preserved footprints left by aurochs — a species of cattle believed to have first appeared on earth 2 million years ago and that went extinct in the 1600s.

“The fact this lasted for 6,000 years and has been smashed through in 25 minutes is an utter shock,” he added.

For its part, Highways England denied its workers had done anything wrong.

"No damage has been caused to archaeological layers," said a spokesman for the government-owned company. "Our assessments so far indicate that construction of the scheme will have no significant effects on the Blick Mead area, and the works have been undertaken in a highly professional manner, with an archaeologist on site and with due care being exercised at all times.”

The Amesbury Museum and Heritage Trust, an organization that preserves and promotes historically significant sites in the area of Blick Mead, described the work of Highways England as "unbelievable and careless destruction."

Traffic moving along the a road bear Stonehenge. Steve Parsons / PA/AP file

The tunnel, part of an effort to solve a decades-old traffic problem at Stonehenge, has been widely criticized by archaeologists and the local community.

Jacques and representatives of Highways England are meeting at the site on Thursday to assess any damage.