BRITAIN (REUTERS) - British author J.K. Rowling is delving back into the world of Harry Potter for a series of short ebooks with new stories about some of her characters from the Hogwarts School of Witchcraft and Wizardry.

Pottermore, the digital publishing and e-commerce world founded by Rowling for fans of the boy wizard, said on Wednesday it would be releasing three short ebooks starting Sept 6.

Called Pottermore Presents, the series is a collection of Rowling's writing for Pottermore.com, as well as new stories about characters including Potter's potions master Horace Slughorn, Hogwarts headmistress Professor Minerva McGonagall and Ministry of Magic bureaucrat Dolores Umbridge.

The ebooks will be available on the Pottermore website as well as through digital book sellers. They are the latest extension of the Harry Potter franchise, which includes seven books, eight movies, three theme park attractions and the sold-out London stage play, Harry Potter And The Cursed Child.

The ebooks, approximately 10,000 words long, are intended for tablets, cellphones and other mobile devices and as a supplement to the original Harry Potter books, which have sold more than 450 million copies worldwide.

"J.K. Rowling's writing in these collections reveals intricate details of her characters' lives, their histories, as well as her inspiration," Pottermore chief executive Susan Jurevics said in a statement.

Fantastic Beasts And Where To Find Them, the first of three Potter spin-off movies, is due for release worldwide in November.