Archaeologists have discovered a secret tomb at the Treasury monument in Petra, Jordan - one of the Seven Wonders of the World.

A long-buried tomb containing the remains of 12 ancient skeletons and grave offerings was found beneath the monument after research teams used remote sensing technology.

The discovery comes more than two decades after similar tombs were found on the other side of the famous monument, which is a UNESCO World Heritage Site and attracts more than a million visitors a year.

The Treasury sits as the center of an entire city carved by hand into the walls of a desert canyon by the Nabataean people about 2,000 years ago.

It is still not clear what its true purpose is.

British and American researchers from the University of St Andrews, the Jordanian Department of Antiquities, and the American Center of Research had been permitted to conduct remote sensing in and around the monument.

They were aiming to assess the condition of the areas around the site using electromagnetic conductivity and ground penetrating radar - but ended up making a much more exciting discovery.

When the survey found what appeared to be underground chambers, the researchers carried out an excavation and found the tomb.

One of the skeletons discovered was grasping the top part of a broken jug that most likely dates to the first century BC.

Richard Bates, a geophysicist and professor at the University of St Andrews, told Sky News' partner network NBC News the remains most likely include both men and women and range in age from children to adults.

The researchers believe the discovery could provide new insight into the Treasury and the people of the Nabataean Kingdom.

"The discovery is of international significance as very few complete burials from the early Nabataeans have ever been recovered from Petra before. The burials, their goods, and the human remains can all be expected to help fill the gaps in our knowledge of how Petra came to be and who the Nabataeans were," Professor Bates said.

Archaeologists found the walls within the tomb were dated to between the mid-1st century BC and the early 2nd century AD.

The excavation of the newly revealed tomb was featured in a two-part episode of the American reality television series Expedition Unknown that aired on Discovery Channel.