So-called Islamic State claims responsibility in the Berlin attack

Berlin's iconic Brandenburg Gate was illuminated in the colours of the national flag in tribute to the victims (AP)

So-called Islamic State (IS) has said one of its militants carried out the lorry attack on a Berlin Christmas market, which left 12 people dead.

The identity of the attacker has not been established and there was no immediate way of verifying the claim.

German prosecutors have freed the only suspect, citing insufficient evidence. He was identified by media only as Pakistani national Naved B.

Officials suggested that a perpetrator or perpetrators might be on the run.

IS said through its news agency that one of its "soldiers" had carried out the attack, in which 49 people were also injured, "in response to calls to target nationals of the coalition countries".

German Interior Minister Thomas De Maiziere reacted cautiously to the claim, saying "several lines of investigation" were being pursued.

Before the suspect was released late on Tuesday, German officials said they could not be sure if he was involved in the attack.

Federal prosecutor Peter Frank told reporters that the style of attack and the choice of target suggested Islamic extremism.