Less than 24 hours after a "disturbed" person rammed his car into a crowd in Muenster, German police have reportedly foiled a terror plot to carry out an ISIS-inspired knife attack at the Berlin half-marathon today.

The German daily Die Welt is reporting that special police forces detained four men in connection with Sunday's sports event.

They said the main suspect was planning to killed participants and spectators with knives.

The main suspect was also reportedly known to Anis Amri - the Tunisian national who carried out the December 2016 Berlin Christmas market atrocity that killed 12 - and had planned to stab to death spectators and runners at the half marathon.

He was arrested in possession of two knives which had been sharpened, the report said.

Berlin police were not immediately available for comment.

German news agency dpa reported that police confirmed arrests in connection with the half-marathon but gave no further details.

Reuters additionally reports that Earlier on Sunday, Interior Minister Horst Seehofer said the government would do everything possible to protect citizens, but added:

“We have again experienced that ... absolute security is unfortunately not possible.”

As a reminder, Amri's attack in Berlin in 2016 had prompted German lawmakers to call for tougher security measures - and shifted Angela Merkel's 'come-one-come-all' immigration stance. No major Islamist militant attack has been carried out in Germany since.