Berlin attack: Massive manhunt underway for truck's driver

A massive manhunt has been launched for the person who was driving the truck which ploughed into a Christmas market in Berlin, killing 12 people dead and leaving 48 injured.

Meanwhile, authorities released a Pakistani asylum seeker who was arrested shortly after the attack, saying they did not have enough evidence to hold him.

As the manhunt continued, ISIS claimed to have inspired the attack. The terror group's affiliated Amaq news agency described the perpetrator as a "soldier of the Islamic State," who had acted in response to calls for attacks in the West.

While German authorities are treating this as a terror attack, there is no evidence of any direct link between the attacker and ISIS, the CNN reports.

Police have appealed to the public for any digital videos and photos they have of the incident or possible suspects. They tweeted Tuesday that they had so far received 508 leads.

After the suspect was released, police are "really back to square one in terms of this investigation,".

According to German media, the man was identified by witnesses as being the driver of the truck at the time of the incident, but police soon ascertained that this was not the case.

A Polish man found shot to death inside the truck has been identified as its original driver, according to German media.

He was not driving during the incident, police said. The gun used to kill him has not yet been recovered.

German Chancellor Angela Merkel said she was "horrified and deeply sad about what happened" during a visit to the scene of the attack.

Monday's attack could cause further political upheaval for Merkel, who has come under criticism over her government's generous acceptance of refugees.

Germany has taken in more than 890,000 asylum-seekers in the past year, a much higher number than other European nations.