SALZBURG, Austria (Reuters) - An Austrian pianist performed two newly discovered pieces by Wolfgang Amadeus Mozart for the first time in public on Sunday in a house where the master composer once lived.

The concerto movement and a prelude were originally judged by their archivist, the International Mozarteum Foundation, to be anonymous works. Further analysis determined they had been composed by Mozart when he was 7- or 8-years-old.

Both pieces were transcribed in the writing of Mozart's father Leopold but the analysis showed he must have done so from what his prodigy child was playing on a piano, the foundation's Mozart researcher Ulrich Leisinger told a news conference.

He said the young Mozart almost certainly asked his father to put the pieces to paper because he could not yet do musical notation, and later made his own corrections.

This was a young composer running riot to show what he was capable of. The piece does contain real technical mistakes and clumsy moments that an old hand like Leopold Mozart would never have made, Leisinger said.

Neither the compositional style nor hasty correction-ridden hand-writing are consistent with Leopold's authorship.

Both pieces were played by pianist Florian Birsak on Mozart's own piano in the Salzburg house where he lived for several years as a young man, and that is now a museum.

The International Mozarteum Foundation was founded as a non-profit organization in 1880 to focus on the life and work of Mozart by holding concerts, running museums and promoting research regarding the composer.

Mozart was born in Salzburg in 1756 and died in Vienna in 1791 at the age of 35.

He began playing piano at an early age and was composing from the age of five, going on to write more than 600 works and becoming one of the most prolific and beloved classical composers.

This is not the first time in recent years that works by Mozart have resurfaced posthumously. Last year a library in Nantes, France, reported finding that a musical score that had been donated by a private collector at the end of the 19th century was a Mozart original rather than a copy as earlier thought.

(Writing by Mark Heinrich; Editing by Alison Williams)