German Chancellor Angela Merkel said Tuesday authorities are assuming a truck attack that killed at least 12 people and injured nearly 50 others at a crowded open air market in Berlin was a terrorist act.
The truck plowed into the market outside the landmark Kaiser Wilhelm Memorial Church Monday evening as Germans celebrated the Christmas season with traditional outdoor festivities. The suspected driver was arrested about two kilometers away, while a second person found inside the truck died at the scene while undergoing medical treatment.
German media reported the suspect was a Pakistani citizen who arrived in Germany about one year ago.
Merkel said it would be "especially hard for us all to bear" if someone who sought protection and asylum was responsible.
"This would be especially despicable for the many, many Germans who day in, day out are active working for refugees as well as for those people who actually need our protection and who make an effort to integrate into our country," she told reporters.
The White House offered condolences in a statement that condemned "what appears to have been a terrorist attack."
Witnesses said the popular Christmas market was packed with tourists and locals when the truck, believed traveling in excess of 60 kilometers an hour, slammed into it. Authorities said the vehicle was loaded with steel beams.
The U.S. State Department had earlier called for caution in market places and other public sites across Europe. A published U.S. travel alert said extremist groups were focusing their attention "on the upcoming holiday season and associated events." It also warned U.S. citizens on the continent to be on the alert for "self-radicalized" extremists, who it said could strike without warning.
The Polish owner of the truck, which had Polish license plates, said he feared the vehicle, driven by a relative, may have been hijacked.
WATCH: Video from the scene
Ariel Zurawski said he last spoke with his cousin several hours before the crash, and was told that the truck was set to be unloaded Tuesday.
"They must have done something to my driver," Zurawski told German TV24.
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Monday's crash bore strong similarities to a truck attack earlier this year in southern France that killed scores of people and wounded many others as France celebrated a national holiday.
French police linked that July 14 attack, which killed 86 people and wounded more than 400 others, to a Tunisian national with reputed links to Islamic State extremists.