The Pakistani man who was arrested after the Berlin truck attack, was released as a result of insufficient evidence, according to the prosecution. The attacker could be still at large, police said earlier.

The German Federal Prosecutor's Office has given a statement about the release of the suspect.

Holger Münch, the head of the federal criminal police office, said at a press conference on Tuesday that “we need to work on the assumption that an armed perpetrator is still at large. As a result of this we are on high alert.”

During a press conference on Tuesday, German Prosecutor General Peter Frank also expressed doubts as to whether the detained Pakistani was the perpetrator, urging investigators to begin their probe under the “assumption that the detained man was not the actual perpetrator and did not belong to the criminal group” that carried out the Berlin market attack.

Earlier Die Welt newspaper cited a high-ranking security source as saying that the Pakistani refugee was not involved in the attack.

"We have the wrong man," Die Welt cited a Berlin police official as saying. "And thus a new situation. The actual perpetrator is still at large and armed, and can inflict more damage."

For your safety! In case of suspicious observations, please don't investigate on your own - it's our job. — PolizeiBerlinEinsatz (@PolizeiBerlin_E) 20 декабря 2016 г.

Earlier Berlin police chief Klaus Kandt also said investigators are unsure if the Pakistani man arrested shortly after the truck attack was actually the driver who rammed the vehicle into a crowd at the Christmas market.

"As far as I know it is in fact uncertain whether that really was the driver," he said.

Despite the heightened security alert, the preparations for New Year's Eve celebrations will continue as planned, Kandt added.

Entrances to all Christmas markets will be guarded by police officers armed with submachine guns, and security barriers will be erected.

Police urged Berlin residents "not to follow dangerous developments on your own," asking them to report any suspicious activity to law enforcement officers.

The temporary arrested suspect denies the offense.

Therefore we are particulary alert.

Please be also alert.#Breitscheidplatz — PolizeiBerlinEinsatz (@PolizeiBerlin_E) December 20, 2016

READ MORE: No doubt Berlin truck incident was terrorist attack – German Interior Ministry

Berlin police tweeted that they are still on alert, after the Pakistani suspect denied any involvement in the truck attack.

"The temporarily-arrested suspect denies the offense. Therefore we are particularly alert. Please be also alert," the police wrote.