Twelve people were killed and more than 45 others injured Monday evening when a 40-ton truck from Poland crashed into a popular outdoor Christmas market in the heart of Berlin and smashed its way about 80 yards through the crowd.
Police said they were still investigating whether it was an intentional attack on the holiday market at the Kaiser Wilhelm Memorial Church, one of dozens of cherished holiday markets across the city where hundreds of people gather for drinks, snacks and a chance to shop for handmade gifts.
U.S. National Security Council spokesman Ned Price said the U.S. condemned the "horrific incident," which he said "appears to have been a terrorist attack."
The incident came on the same day that Russia's ambassador to Turkey was shot to death in Ankara, and three people were shot and wounded near a Muslim prayer center in the Swiss city of Zurich.
"Today there were terror attacks in Turkey, Switzerland and Germany -- and it is only getting worse. The civilized world must change thinking!" U.S. President-elect Donald Trump said on Twitter.
The German federal prosecutor's office quickly took control of the case. Police, who initially said it appeared to be a deliberate attack, said a suspect who fled from the truck had been captured and was being questioned. A second person was found dead in the passenger seat of the truck, authorities said.
Across Germany, political leaders expressed anxiety over the incident and the possibility of further dangers.
"Our worst fears have come true with this suspected attack on the Christmas market in Berlin," said Stephan Mayer, a senior member in Parliament for Chancellor Angela Merkel's conservative party. "We've got to review the security for Christmas markets across Germany, and be ready to possibly accept that they can't take place anymore."
The incident revived memories of the attack in July in Nice, France, when a truck driver plowed through a national holiday crowd and killed more than 80 people during Bastille Day celebrations.
"We're very much hoping that this isn't an attack as we've been fearing for weeks," said Berlin Mayor Michael Mueller. "It's depressing to see that we've now experienced what our friends in other cities have gone through in the past."
There were reports in the German media that the truck, which was loaded with steel rods, had been hijacked and the Polish driver killed. But Berlin officials did not confirm those accounts.
"That's speculation at this point," Berlin's Interior Minister, Andreas Geisel, told a German TV network. "We still don't know whether this was an accident or an attack. It could be either."
Berlin police said they were investigating the possibility that the truck had been stolen from the Polish truck company that owned it. German Interior Minister Thomas de Maiziere told ARD TV that the Polish company had lost contact with its driver about 4 p.m. — four hours before the attack.
Emma Rushton, a British woman who was drinking mulled wine with friends near the scene and witnessed the attack, said she saw the top of the truck as it plowed through the crowd at about 40 mph.
"It wasn't an accident," she told the BBC. "It didn't feel like an accident."
Mike Fox, visiting from the British city of Birmingham, said there were no signs that the truck had attempted to stop.
"It was careering in and bashing into stalls where people were facing the stalls, and then carried on through," Fox told reporters. "It didn't look like it was stopping. There was no brake sounds. It was clearly going straight on through."
Merkel expressed her sorrow for the victims, her spokesman Steffen Seibert said on Twitter. Merkel has faced criticism for opening the country's doors to more than a million refugees in the last year, and her advisors and diplomats have expressed fears that a major terrorist attack caused by an immigrant could severely damage her hopes of winning a fourth term in September's election.
In Washington, U.S. officials pledged their help in the investigation.
"The United States condemns in the strongest terms what appears to have been a terrorist attack on a Christmas market in Berlin," Price said in a statement.
"Germany is one of our closest partners and strongest allies, and we stand together with Berlin in the fight against all those who target our way of life and threaten our societies."
German TV networks showed police and rescue workers moving around a damaged black truck with the front windows badly smashed. TV network RTL reported that the truck's headlights were switched off as it drove through the crowd.
Germany has not been hit by major terrorist attacks on the scale that France and Belgium have seen in the last year, but authorities have been on high alert for attacks like those in Paris, Nice and Brussels over the last 13 months.
The government and police authorities have long expressed fears that the beloved Christmas markets that pop up in towns and cities across the country in December were especially vulnerable to attacks. The myriad markets, where large crowds gather in relatively compact areas in town centers and squares, are almost impossible to protect without destroying their celebratory nature.
Police spokesman Winfrid Wenzel described the carnage caused by the truck, which left the road and veered up onto the curb and into the market where dozens of small handmade wooden stalls were shattered.
"The truck carved a swath between the wooden stalls of between 60 to 80 meters," Wenzel told reporters. "Witnesses said that a man fled from the cabin of the truck. A second man found in the cabin of the truck is dead. We had a description of the man who fled and were able to capture a person matching that description near the Victory Column monument."
Kirschbaum is a special correspondent.
5:05 p.m.: The article was updated with a new death toll.
4:20 p.m.: The article was updated with an additional witness, a report that the owner of the truck had lost contact with the driver, and a tweet from Donald Trump.
3:40 p.m.: The article was updated with a report from an eyewitness.
3:05 p.m.: The article was updated with additional details from the investigation and a statement from the U.S. National Security Council spokesman.
12:55 p.m.: This article was updated with Times reporting.
12:45 p.m.: This article was updated with a witness account.
12:20 p.m.: This article was updated with news that nine people have died.