WORLD
The attack also left 48 people injured.
The Berlin police chief said on Tuesday it was not clear if the Pakistani man arrested after a deadly trunk rampage at a Christmas market was the driver of the vehicle. The attack left 12 people dead.
"As far as I know it is in fact uncertain whether that really was the driver," said Berlin Police President Klaus Kandt.
Berlin police said on Twitter that they were being vigilant as the suspect had denied involvement in the incident, which police have said was a deliberate attack.
"The temporary arrested suspect denies the offense," Berlin police tweeted in English. "Therefore we are particularly alert. Please be also alert," they urged the public.
Earlier, Die Welt newspaper citing senior security sources reported that German police think that the man arrested was not the actual perpetrator. "We have the wrong man," said a senior police chief. "And therefore a new situation. The true perpetrator is still armed, at large and can cause fresh damage," the paper quoted the source as saying.
In the deadly incident, the truck smashed into wooden huts serving mulled wine and sausages at the foot of the Kaiser Wilhelm memorial church, one of west Berlin's most famous landmarks, on Monday evening. Forty-eight people were injured, 18 severely.
Chancellor Angela Merkel told reporters: "There is much we still do not know with sufficient certainty but we must, as things stand now, assume it was a terrorist attack."
She added: "I know it would be especially hard for us all to bear if it were confirmed that the person who committed this act was someone who sought protection and asylum."