President-elect Donald Trump condemned the attack in Berlin, after a driver ploughed a lorry through a crowded Christmas market in the centre of Berlin.
At least 12 people died in the alleged attack, while almost 50 others sustained injuries. The driver fled the scene, but police say they have arrested a suspect they believe was at the wheel. The passenger in the vehicle died at the scene.
The incident was reminiscent of an attack in Nice, France, when a lorry driver drove through a crowded outdoor celebration for Bastille Day on 14 July. Isis later claimed responsibility for the attack, calling the truck driver a “soldier”.
But the motivation behind Monday’s deadly episode remains unclear. Still, the President-elect was quick to blame Isis and radical Islamist groups – before investigators could issue any confirmation.
“Our hearts and prayers are with the loved ones of the victims of today's horrifying terror attack in Berlin,” Mr Trump said. “Innocent civilians were murdered in the streets as they prepared to celebrate the Christmas holiday.”
He added: “Isis and other Islamist terrorists continually slaughter Christians in their communities and places of worship as part of their global jihad.
“These terrorists and their regional and worldwide networks must be eradicated from the face of the earth, a mission we will carry out with all freedom-loving partners.”
On Twitter, he elaborated on his warning.
“Today there were terror attacks in Turkey, Switzerland, and Germany – and it is only getting worse,” he wrote. “The civilised world must change thinking!"
But German officials have warned against using such extreme language before police could confirm the reason behind the incident.
"I don't want to use the word 'attack' yet at the moment, although a lot speaks for it," said Germany's interior minister Thomas de Maizière.
"There is a psychological effect in the whole country of the choice of words here, and we want to be very, very cautious and operate close to the actual investigation results, not with speculation."