A migrant from Pakistan was identified Tuesday as a suspect in a truck attack on a crowded Christmas market in Germany's capital.
He was arrested not far from the scene of Monday night's carnage, which left 12 people dead and wounded nearly 50 others.
He entered the country last year and had applied for asylum, Interior Minister Thomas de Maiziere told reporters, adding that other people may be involved. He said the suspect in custody had denied responsibility.
A temporary accommodation center for migrants was raided overnight by special operations police, but no further arrests were made.
Chancellor Angela Merkel, who has faced political pressure over open-arms policy for refugees, earlier said it would be "hard for us all to bear" if the perpetrator "was someone who sought protection and asylum."
She added: "I have no simple answers. We cannot live without these shared moments in public spaces. We must not be limited by fear of evil. We will live as we wish in Germany — free, together and openly."
More than 2.1 million immigrants were registered in Germany in 2015, according to provisional results from the Federal Statistics Office. That represented a 46 percent year-on-year increase and is almost as many people who live in Houston, the fourth-largest city in the U.S.
Federal prosecutors took over investigation after the truck was driven into Breitscheidplatz, a popular public square where tourists and locals were enjoying a traditional pre-Christmas evening.
Police said the truck was "intentionally directed" into the crowd in an act of "probable terrorism."
Local media identified the suspect as "Naved B.," a 23-year-old who entered Germany via Austria on December 31, 2015. He was reportedly already known to police for minor offenses. Those reports could not immediately be confirmed by NBC News.
De Maiziere said only a few of the victims had been identified so far, and that 18 of the 48 wounded had suffered severe injuries.
Among the dead was a Polish man found shot to death inside the cab of the stolen truck, which registered in Poland. The weapon has not been found.
Christmas markets in Berlin were closed Tuesday as a mark of respect for the victims, but the interior ministry said other events around the country would take place with increased security measures.
Emma Rushton, an English tourist who witnessed the incident, told NBC News that she heard the "terrifying" crash while she was with a friend at the Christmas market.
"People were bleeding. There was lots of blood and lots of crying," she said.
Rushton said she that thought the truck was going about 40 mph and that "there was no way it was just a veer-off-the-road accident."
Other witnesses said victims were crushed.
The owner of the truck said he feared the vehicle may have been hijacked. Ariel Zurawski said he last spoke with the driver, his cousin, around noon on Monday.
The driver told him he was in Berlin and scheduled to unload Tuesday morning. "They must have done something to my driver," he told TVN24.
The crash came less than a month after the State Department warned U.S. citizens to exercise caution at overseas holiday festivals and outdoor markets in light of the heightened risk of terrorist attacks throughout Europe.
German officials said Merkel spoke with President Barack Obama by phone Tuesday about the Berlin attack.
"President Obama assured the German chancellor that the United States would support Germany in the investigation," Merkel's spokesman Steffen Seibert said in a statement.