German banker Thilo Sarrazin, who caused outrage with a book blaming Islam for the poor integration of Muslims, has been threatened with murder on social networking website Facebook, media reported Tuesday.

Police are investigating the threat, German daily Bild reported.

The controversial 65-year-old banker has been placed under police protection and was accompanied by four officers at a speaking engagement Monday.

After the engagement, at which Sarrazin defended his ideas about immigration and the German welfare state, Sarrazin was verbally abused by a man as he made his way to his vehicle.

He has also stirred controversy by declaring there was a 'Jewish gene' and is facing possible dismissal from his job at the German central bank.

His book 'Germany Abolishes Itself' has become an instant bestseller since its launch last week.