This 15th-century portrait of a young woman is believed to be by Leonardo da Vinci, experts say. (Alessandro Vezzosi/Museo Ideale Leonardo Da Vinci/ Associated Press)

A drawing that sold for just $21,850 US a decade ago may be a portrait by Renaissance master Leonardo da Vinci.

Art experts from Italy and the U.S. say the Nuptial Portrait of a Young Woman, originally believed to be by an unknown German artist, is actually the work of a skilled left-handed artist such as Leonardo.

The portrait was done to attract a suitor for the unidentified woman, believed to be from the Tuscan town of Vinci, Leonardo's home.

And it may have been successful, as the portrait spent some time in Germany. One Italian expert believes Leonardo travelled with the newlyweds across the Alps to the Tyrol.

The woman's hometown is identifiable by her dress, which has Vinci knots on the sleeve, a fashion from the town. Her hair is tied in a style often seen in portraits by Leonardo, including the Mona Lisa.

Experts studied the portrait for more than a year before concluding it may have been done by Leonardo. The decision escalates the value of the work to millions of dollars.

"The intensity, quality and purity of the work make the recognition of it as a Leonardo the obvious conclusion," said Alessandro Vezzosi, the director of the Da Vinci museum, in the artist's hometown of Vinci near Florence.

"The most telling clue is the left-handed style — which is typical Leonardo — and every element points to Leonardo. It is an extraordinary work."

The 24-centimetre-by-33-centimetre pen and ink on parchment shows a woman in Renaissance dress facing left.

"The detail in the eye is very limpid as Leonardo strongly believed in making the eyes look like the windows of the soul; it emphasizes the interior grace and character of the subject," Vezzosi said.

"It's very probable that this work was commissioned by the lady in the picture and sent to a prospective groom to show off her beauty."

He said the picture was probably painted around the mid-1480s, when Leonardo was working out of Milan. However, carbon dating has yet to be performed on the portrait.

Several other art experts from around the world have backed the supposition that it is a Leonardo.

'Extremely fine execution'

A Paris-based lab that studied another masterpiece attributed to Leonard, Lady With an Ermine, has performed analysis on the drawing.

Carlo Pedretti, director of a centre for Leonardo studies at the University of California in Los Angeles, and Nicholas Turner, former curator of drawings at the J. Paul Getty Museum and the British Museum, also say the work is likely Leonardo's.

The work is of "extremely fine execution," Turner said. "There were only very few artists of that calibre then.

"When I first saw the painting, I was struck by two possibilities that it was a very beautiful fake, or an unknown Leonardo," he said.

"What I noted was the skill of the shading around the face, which I believe can only have been drawn by a left-handed artist such as Leonardo."

Pedretti calls the find the most important since Lady with An Ermine, which was identified as a Leonardo early in the 19th century.

The painting is owned by a New York collector who wishes to remain anonymous.

With files from the Associated Press