Scientists have discovered a secret chamber inside the Great Pyramid of Giza that is believed to date back millennia, the Nature journal reported on Thursday.
The secret chamber, which could date back to 2560 BC, is estimated to be some 30 metres (98 feet) long and could help explain how the tomb of the Egyptian pharaoh Khufu -- after whom the pyramid was named -- was built, the BBC reported.
The 4,500-year-old pyramid was built during the reign of Khufu or Cheops, the second pharaoh of the Fourth Dynasty of the Old Kingdom of ancient Egypt.
"Despite being one of the oldest and largest monuments on Earth, there is no consensus about how (Khufu) was built," researchers said.
"To better understand its (Khufu's) internal structure, we imaged the pyramid using muons, which are by-products of cosmic rays that are only partially absorbed by stone," they said.
The discovery was led by researchers from Egypt, France and Japan.
The Khufu monument or the Great Pyramid contains three large interior chambers and a series of passageways, the most striking of which is the 47-metre-long, 8-metre-high grand gallery.
The newly-identified feature is said to sit directly above this and have similar dimensions, scientists said.
"We don't know whether this big void is horizontal or inclined. We don't know if this void is made by one structure or several successive structures," said Mehdi Tayoubi from the HIP Institute, Paris.
"What we are sure about is that this big void is there, that it is impressive... and that it was not expected as far as I know by any sort of theory," he said.
Khufu contains compartments that experts believe may have been incorporated by the builders to avoid collapse by relieving some of the stress of the overlying weight of stone.