The so-called "Islamic State" (IS) on Tuesday said the driver of the truck that plowed into a Christmas market in Berlin on Monday evening was "targeting citizens of the Crusader coalition," according to the group's news agency Amaq. 

Earlier, German prosecutors announced the release of a 23-year-old Pakistani detained in connection with the truck attack, citing a lack of evidence.

On Tuesday night, following the announcement that the suspect had been released, German Interior Minister Thomas de Maiziere told broadcaster ZDF that "it is true that one cannot rule out that the perpetrator is still at large." He also warned that it was too early to draw political conclusions from the incident.

Authorities had arrested the asylum seeker on suspicion of driving the truck, which killed 12 and injured at least 48. 

'Wrong man' detained

Even before de Maiziere made his statement, Berlin police had admitted that they may have apprehended the wrong suspect and warned the public to remain attentive and vigilant. 

"As far as I know, it is in fact uncertain whether that really was the driver," Berlin's police chief Klaus Kandt said at a press conference.

Germany's "Die Welt" newspaper had also quoted security sources as saying the arrested man was not believed to be the perpetrator.

A police spokesperson reportedly told the paper: "We have the wrong man, and therefore a new situation. The true perpetrator is still armed, at large and can cause fresh damage."

Speaking to German news agency dpa following the press conference, Kandt said investigators were continuing to inspect the truck used in the attack, searching for fingerprints, blood and smudge marks. "I estimate that the current investigation will take somewhat longer," he said, adding that it could take a few days before new evidence comes to light.

A Polish man who was in the passenger seat of the crashed truck was found shot dead at the scene. 

'An act of terrorism'

Germany's two top prosecutors confirmed Tuesday that investigators are indeed treating the incident as an act of terrorism. Prosecutor Peter Frank said that, given the target and nature of the attack, the incident pointed towards Islamist extremist motives.

Frank said the attack was reminiscent of July's terrorist attack in Nice, France, and of the "modus operandi" deployed by Islamist terror groups. 

However, echoing Berlin's police officials, Frank also acknowledged that the detained suspect "may not have been the perpetrator or belong to the group of perpetrators."

German Chancellor Angela Merkel, who visited the scene of the attack on Tuesday afternoon, also referred to the incident as a "terrorist act." Speaking before the police made their admission about the detained suspect, Merkel acknowledged that the crime might have been committed by an asylum seeker. 

Risk remains high

The head of Germany's Criminal Police Agency, Holger Münch, said he could not rule out if further suspects were still at large, and therefore warned of further attacks on the back of Monday's incident. In the aftermath of such an event, "there's always a heightened risk of significant further attacks," he said. 

"We are naturally on high alert and are investigating in all directions," Münch added.

He also revealed that six of the 12 people killed have been identified as Germans. He could not, however, identify the nationalities of the other six.

New Year's celebrations to go ahead

Also speaking Tuesday, Berlin's State Interior Minister Andreas Geisel confirmed that the city's New Year's Eve celebrations will go ahead under an increased security presence. Every year, hundreds of thousands of revelers ring in the New Year in front of Berlin's Brandenburg Gate.

He said the city will review all of its security measures before the celebrations on December 31.

dm, blc/rc (dpa, AP, Reuters)