Three sketches possibly drawn by Leonardo da Vinci have been found on the back of one of the master's major works.
Describing the find as "an exceptional discovery", the Louvre museum said in a statement that the drawings were found when da Vinci 1500s oil Virgin And Child With St Anne was undergoing routine examination in the laboratory.
"When taking down the work - an oil on wood - a curator from the paintings department noticed two barely visible sketches on the back, representing a horse's head and half a skull," the Louvre said.
Further examination revealed a third sketch, a Baby Jesus and Lamb.
"This is an exceptional discovery as sketches on backs of works are very rare and there is no known example of one from Leonardo to this day," it added.
The sketches, which are practically invisible to the naked eye, had never been noticed in the past when handling the extremely heavy work.
The work is made of four vertical planks of poplar backed by two horizontal wooden crosspieces.
After noting the presence of the two sketches, the back of the work was sent for further examination and the third sketch seen.
"While the style of the sketches evokes Leonardo da Vinci, research is continuing," the Louvre said.