The fossilised skeleton of an unidentified type of dinosaur is set to be auctioned in Paris in June, and could fetch up to €1.8 million, auctioneers said.

Almost nine metres long, the skeleton is unusually complete, at almost 70 percent whole.

It is believed to be from the carnivorous, theropod group of dinosaurs, which had hollow bones and three-toed feet, said Eric Mickeler, a paleontological expert working with auction house Aguttes.

But beyond that scientists are still stumped and have spotted differences with known species, he added.

"Nothing else is known," Mickeler said.

The skeleton, now on show in the French city of Lyon to possible buyers such as museums or private collectors before the June 4 auction, is estimated to be worth between €1.2 million and €1.8 million.

It was found in Wyoming, in the United States, in 2013 and belongs to an unnamed British businessman.

It will be installed on the first floor of the Eiffel Tower for the sale. Potential buyers can bid in euros or in digital currency bitcoin.