BERLIN (Reuters) - German police said they detained several people in Berlin who they suspected of planning a crime linked to Sunday’s half-marathon, and newspaper Die Welt said one was suspected of planning a knife attack at the popular event.

Berlin police said in a statement they had detained suspects aged between 18 and 21 after searches in the districts of Charlottenburg-Wilmersdorf and Neukoelln in the capital. They did not say how many people they detained.

“Because of the ongoing investigation, no further information can be given at the present time,” the police added in their statement.

Die Welt said in its online edition the police had detained four men, one of whom they suspected of planning knife attacks at the half-marathon.

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 biggest in Germany.

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

Kenyan Erick Kiptanui clocked a course record of 58 minutes, 42 seconds, equaling the fastest time in the world this year, the race’s organizers 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.