A scruffy crate caught the eye of UK border guards. When they prised it open they found a stolen ancient carving worth $37 million.

• The British Museum will display a rare Iranian carving that was seized by border authorities in London.
• The fragment of the Sasanian rock relief is worth more than $37 million, The Guardian reported.

A 2,000-year-old Iranian carving will go on display at the British Museum after border authorities seized it in the UK before the rare treasure could be sold on the black market, The Guardian reported on Saturday.

The fragment of an ancient Sasanian rock relief is likely worth more than 30 million pounds (about $37 million), according to experts, and has never previously been documented.

At Stansted Airport in London, border guards became "suspicious" when they noticed the "haphazard packaging" concealing the carving, according to The Guardian's report.

Representatives for the UK Border Force did not immediately respond to Insider's request for comment sent outside regular business hours on when the sculpture was seized.

The sculpture depicting a male figure, carved in Iran in the 3rd century, is over three feet tall. It appeared to have been removed from its original place on a cliff with an angle grinder — a power tool used to cut various materials.

"We almost never come across a case of something being cut out of the 'living rock.' That's a level of brutalism that surpasses anything," St John Simpson, a senior curator, and archaeologist in the British Museum's department of the Middle East, told the Guardian.

"You've even got felt-tip marks on the back before they've used an angle grinder to slice diagonally behind it and across the top. It was then packed in an incredibly bad manner, in a small, almost unpadded crate held together with nails," he said.

The unique sculpture carved from calcareous limestone dates back to the Sasanian empire — between 224 and 651 AD. There are only about 30 known Sasanian rock reliefs, almost all from Iran's Fars province.

The British Museum repaired the "incredibly valuable" relief because it had broken due to its poor packaging.

"It is stunningly attractive. The valuation could be anything, really. We're talking £20m to £30m-plus. There's never been anything like it on the market," Simpson told The Guardian.

The museum received permission from Iran to put it on display for several months before returning it to the National Museum in Tehran.

While authorities have investigated the case of the stolen antiquity, no arrests have been made so far, per the Guardian.