British police revealed, on Tuesday, that they had opened an investigation into a package containing uranium that was seized at London's Heathrow Airport.

Border agents spotted the parcel during a regular inspection on December 29, as per authorities.

According to The Sun, which first reported the story, the box originated in Pakistan and arrived on a flight from Oman.

The uranium was found in a shipment of scrap metal and investigators were looking into whether it was the result of "poor handling" in Pakistan, the BBC reported.

"I want to reassure the public that the amount of contaminated material was extremely small and has been assessed by experts as posing no threat to the public," police commander Richard Smith said in a statement as quoted by British media.

"Although our investigation remains ongoing, from our inquiries so far, it does not appear to be linked to any direct threat," he added.

To fly dangerous cargo, including uranium, strict standards must be followed, including loading the nuclear material into the base of units in the cargo hold and maintaining a minimum distance between the radioactive material and the cabin above.

It is worth noting that Uranium is a naturally occurring element. Once refined or enriched, it can be used in nuclear applications. This is accomplished through the use of centrifuges, which are machines that spin at supersonic speeds.

Low-enriched uranium can be used to make nuclear fuel for commercial power plants.

Highly enriched uranium is utilized in research reactors and has a purity of 20% or more. 90% enriched uranium is used in nuclear weapons.