Art detectives have said they believe they have found traces of a Leonardo Da Vinci masterpiece on a hidden wall in a palace in Florence that has not been seen in over four centuries.

The traces were collected using tiny probes introduced into a wall covering the original surface in a lavish hall in the Palazzo Vecchio and contained a black pigment also used in his "Mona Lisa", project organisers said.

The research is the result of a decades-long quest by San Diego University art history professor Maurizio Seracini, who was featured in Dan Brown's bestseller "The Da Vinci Code" and used cutting-edge technology in the project.

"These data are very encouraging," Seracini said.

"Although we are still in the preliminary stages of the research and there is still a lot of work to be done to solve this mystery, the evidence does suggest that we are searching in the right place," he said.

The probes also discovered red lacquer and brown pigment on the hidden wall and an air gap between the old wall and the new wall built in front of it.

Historians at a press conference in the Italian city of Florence however stressed their research was "not conclusive" and further chemical analysis needed to be carried out.

Da Vinci began his fresco "The Battle of Anghiari" - a historic clash in 1440 between Milanese and Florentine forces - in the Hall of the Five Hundred in 1505 but never finished it because the colours began to run.

The fresco was nevertheless praised by Da Vinci's contemporaries for what art historian and fellow painter Giorgio Vasari called its "graceful beauty" and Flemish Baroque painter Peter Paul Rubens drew a famous copy of it.

The Rubens sketch shows a bloody scene of horsemen battling with swords drawn and trampling over infantry men - their faces contorted with rage and their muscled horses entwined with eyes bulging out with fear.

Some historians believe Vasari built a wall in front of the fresco so as to preserve Da Vinci's efforts out of respect for the renowned master and then painted his own work, "The Battle of Marciano", on the new wall in 1563.

"The data from chemical analysis, while not conclusive, suggest the possibility that the da Vinci painting, long assumed to have been destroyed in the mid-16th century... might exist behind the Vasari," organisers said.

The research, which was partly sponsored by National Geographic, has been controversial however and has even been investigated by police because researchers bored six small holes into Vasari's work to reach the hidden wall.

The technology used in the project was developed by a senior US nuclear physicist, Robert Smither, who came up with a special camera to generate high-resolution images of a cancer's location in the human body.