BEIJING (Reuters) - Shanghai Masters organizers have increased security for the tournament starting on Saturday after an online threat to decapitate world number one Roger Federer, the Shanghai Youth Daily newspaper reported on Friday.

"On October 6 I plan to assassinate Federer in order to exterminate tennis," read a post by "Blue Cat Polytheistic Leader 07" on a Federer fan website on September 25, the newspaper's website said.

The paper said the post was accompanied by a "very scary" computer modified image showing a decapitated Federer.

Federer may go directly from the airport's VIP arrival hall to his hotel as part of the precautions, Yang Yibin, the tournament director, told the paper in an interview earlier in the week. It said Shanghai police were investigating.

Local journalists said Shanghai municipal authorities had told local media not to report the issue.

(Reporting by Lucy Hornby and Langi Chiang; additional reporting by Aly Song in Shanghai; editing by John Mehaffey)