A 23-year-old asylum seeker of Pakistani origin named Naved B has been arrested under suspicion of carrying out the truck attack on a Christmas market in Berlin, according to German media reports.
Although there has so far been no official confirmation, the suspect was reportedly picked up around one and a half miles away from the scene of the attack, near the Victory Column monument in the city.
Berlin's public radio station RBB-Inforadio cited an unnamed security source as saying that the suspect was a Pakistani citizen who entered Germany on December 31, 2015.
There were mixed reports on the details however. News agency dpa, also citing unnamed security sources, said that he came to Germany as a refugee in February 2016.
Meanwhile Berlin's Tagesspiegel newspaper reported that the man was known to police for minor crimes.
Berlin police have so far declined to confirm the identification of the man as the alleged attacker, but a police spokesman said the man was being interrogated.
According to the Welt daily newspaper, police raided a large shelter for asylum-seekers at Berlin's defunct Tempelhof airport overnight, withfour men reportedly questioned but not arrested.
The truck crashed into people gathered around wooden huts serving mulled wine and sausages at the foot of the Kaiser Wilhelm memorial church, which was left as a ruin after World War Two, in the heart of former West Berlin on Monday evening.
"Our investigators assume that the truck was deliberately steered into the crowd at the Christmas market at Breitscheidplatz," police said on Twitter.
"All police measures related to the suspected terrorist attack at Breitscheidplatz are progressing at full steam and with the necessary diligence," police said.
The incident evoked memories of an attack in Nice, France in July when a Tunisian-born man drove a 19-tonne truck along the beach front, mowing down people who had gathered to watch the fireworks on Bastille Day, killing 86 people. That attack was claimed by Islamic State.
Interior Minister Thomas de Maiziere had previously said there were indications that the incident in Berlin was an attack.
Police said that the man found dead in the truck was a Polish citizen but added he was not in control of the vehicle. The nationality of the suspected driver, who fled the crash scene and was later arrested, was unclear, they said.
Local broadcaster rbb cited security sources as saying the arrested truck driver came to Germany via Passau, a city on the Austrian border, on December 31, 2015. It cited the sources as saying the man was born on January 1, 1993 in Pakistan and was already known to police for minor offences.
If that is confirmed, it could further worsen sentiment toward migrants in Germany, where more than a million people fleeing conflict and poverty in the Middle East, Africa and elsewhere have arrived this year and last.
The record influx has hit Chancellor Angela Merkel's popularity ratings and boosted support for the anti-immigrant Alternative for Germany (AfD). Senior AfD member Marcus Pretzell blamed Merkel for the attack on Twitter.
Austrian Interior Minister Wolfgang Sobotka said on ORF radio on Tuesday that he had told the heads of Austria's regional police forces to intensify surveillance measures, although there was no concrete evidence that an incident was about to happen.
Sobotka also called for biometric and fingerprint checks to be introduced along the Balkan route to better control foreign jihadist fighters' movements.
Berlin police are investigating leads that the truck had been stolen from a construction site in Poland. They have taken the truck for a forensic examination.
Additional reporting by Reuters.
