UPDATE 2:37 p.m. EST:
The Islamic State, also known as ISIS, has claimed responsibility for Monday night's attack on a Christmas market in Berlin, Germany, according to the Washington Post.
The terrorist group's Amaq news agency said in a statement that "the person who carried out the truck run over attack in Berlin is a soldier of the Islamic State and carried out the attack in response to calls for targeting citizens of the Crusader coalition."
The Associated Press contributed to this update.
UPDATE 1:09 p.m. EST:
The man originally arrested in the deadly Berlin Christmas market attack has been released, city police said.
Germany's chief prosecutor said there was not enough evidence to pursue a case.
UPDATE 9:28 a.m. EST: The driver in the deadly Berlin attack may still be at large, police said.
UPDATE 7:46 a.m. EST:
Berlin police chief Klaus Kandt said police have not confirmed whether or not "Naved B." was actually the driver in the attack that killed 12 people at a Christmas market on Monday.
The man accused of driving a truck into a crowded Berlin Christmas market, killing 12 people and injuring dozens, has been identified by local German media as a 23-year-old Pakistani refugee.
"Naved B" had been living in a refugee center and was detained Monday night, The Independent reports. Police have not confirmed his role in the incident.
Officials are investigating the incident as a terror attack. Local media reported the man was a known petty criminal, but was not a suspected terrorist.
BREAKING: Germany's top security official says there is "no doubt" that Berlin truck incident was an attack.— The Associated Press (@AP) December 20, 2016
Security officials said Tuesday there was "no doubt" the incident was deliberate.
Here's the scene of the incident and the resulting memorials.
The truck was originally driven by a Polish citizen who was later found dead inside the truck. The Brandenburg Ministry of the Interior said the Polish man was likely shot.
The German interior ministry urged the traditional open-air markets outside the city to stay open. The Berlin markets are closed for a day of mourning.
The incident is likely to exacerbate tensions in Germany over refugees. The nation has accepted more than one million refugees since 2015, but many residents believe they have caused a spike in crime.
Chancellor Angela Merkel was once very open to refugees but is making concessions to conservative opponents, such as supporting a ban on burqas. She said if the attacker was confirmed to be a refugee, it would be "sickening."
How can we live with the fact that a murderer can bring death to so many while they take a happy walk across a Christmas market?
Denmark and Norway have stepped up security at Christmas markets in their capitals following the attack, as has New York City.
London police said they are reviewing security plans for holiday events to prevent a similar tragedy.
The Associated Press contributed to this report.