The newspaper said the four men were linked to Anis Amri, a Tunisian man with Islamist militant ties who killed 12 people in an attack in Berlin in December 2016 when he hijacked a truck and drove it into a crowded marketplace.

In its unsourced report, Die Welt said the main suspect was known to Amri and had planned to stab to death spectators and runners at the half-marathon.

The suspect had in his possession two knives which had been especially sharpened for this purpose, the report said.

A record of 36,000 athletes entered the 38th edition of the Berlin half-marathon, the largest in Germany.

Thousands of people lined Berlin streets to watch the event, which ended with no reported incidents.

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Kenyan Erick Kiptanui clocked a course record of 58 minutes, 42 seconds, equalling the fastest time in the world this year, the race's organisers said on their website.

Amri's attack in Berlin in 2016 prompted German lawmakers to call for tougher security measures. No major Islamist militant attack has been carried out in Germany since.

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."

Seehofer was speaking in Muenster, where a man drove a camper van into a group of people sitting outside a restaurant on Saturday, killing two of them before shooting himself dead.

Authorities have said the attacker was a 48-year-old German citizen with mental health problems and that there was no indication of an Islamist militant connection.

Reuters