Harry Potter author J.K. Rowling is working on a crime novel, says a British newspaper. 

The Sunday Times quoted Ian Rankin, author of the Inspector Rebus books and a neighbour of Rowling's in Edinburgh, as the source for the report.

J.K. Rowling, shown reading at the launch of Harry Potter and the Deathly Hallows in London on July 20, has been spotted writing in cafes in Edinburgh.
(Jamie Turner/Associated Press)

"My wife spotted her writing her Edinburgh criminal detective novel," said Rankin, who added Rowling has been seen at cafes in Scotland working on her new project.

"It is great that she has not abandoned writing, or Edinburgh cafes," said Rankin, in reference to Rowling's habit of writing her first few Potter books at cafes to save on the heating bill at home.

Back then, she was a single mother. Now she's worth about $1 billion US.

The seventh and final installment of the wizard-in-training books was released July 21 and gobbled up by a worldwide audience. Harry Potter and the Deathly Hallows became the fastest-selling book of all time, with more than 11.3 million volumes sold in the first 24 hours in the USA, UK and Germany alone.

Her previous six books in the series have sold 325 million worldwide.

Days after the release Rowling divulged she was working on two manuscripts: "One is for children and the other is not for children," she revealed in an interview with USA Today.

"I think I've done my fantasy. To go and create another fantasy universe would feel wrong," said the 41-year-old author.

Rowling also said the success of the Harry Potter series has liberated her from financial worries.

"The idea of just wandering off to a cafe with a notebook, and writing and seeing where that takes me for a while is just bliss. Heaven. No pressure."

With files from the Associated Press