Berlin authorities said they arrested six people on Sunday over an alleged plot to carry out a "violent crime" at the German capital's half-marathon which attracted 36,000 runners.
Prosecutors and police said in a statement they had received "isolated indications that those arrested (Sunday) between the ages of 18 and 21 may have been involved in planning a violent crime in connection with this event".The security authorities said that on that basis and after a deadly van rampage on Saturday in the western German city of Muenster, they decided to mount the raids against the suspects.
"Due to the still ongoing investigation, no further information can be provided at this time," they said.
The statement spoke only of "several" arrests and searches of flats and two vehicles in Berlin.
But a tweet by the police mentioned six arrests carried out by special forces.
The half-marathon went off early Sunday without incident, drawing large crowds amid warm summer sunshine.
Berlin's top security official, Andreas Geisel, had said earlier that the capital of 3.5 million people would need to review its precautions for the half marathon following the Muenster attack in which two people were killed.
Some 630 police officers were deployed to guard the race.
Authorities believe the 48-year-old German perpetrator, who shot himself after the Muenster attack, had mental health problems and was not politically motivated.
A report by daily newspaper Die Welt which police did not confirm said that the main suspect in the Berlin probe had links to Tunisian asylum-seeker Anis Amri, who carried out a deadly truck attack on a Christmas market in the German capital in December 2016.
In Germany's worst jihadist attack to date, Amri hijacked a truck and murdered its Polish driver before killing another 11 people and wounding dozens more by ploughing the heavy vehicle through the crowd.
He was shot dead by Italian police in Milan four days later while on the run.