A Pakistani refugee detained on suspicion of carrying out a deadly lorry attack on a Berlin Christmas market has been released from custody, the German authorities said last night, leaving one or more perpetrators still at large.

The federal prosecutor's office in the city of Karlsruhe said that investigations had failed to prove conclusively that the 23-year-old committed any crime.

Authorities said the man had provided a considerable amount of information during questioning, but he denied any involvement in the Monday evening attack.

Witnesses who claimed they had followed the man when he fled the crime scene had not had an uninterrupted view of him, and there was no recording of him in the cabin of the lorry, investigations showed.

"We've got the wrong man and therefore a new situation. The true perpetrator is still armed, on the loose and can do fresh damage," German newspaper Die Welt cited a police official as saying earlier in the day.

Writing on Twitter, German police urged Berliners to be "particularly alert."

The attack at the Christmas market in the west of the city left at least 12 dead and nearly 50 injured, 24 of whom have been released from hospital, German police said.

The Islamic State extremist group, via its Aamaq Agency outlet, claimed responsibility, saying the attacker was a "soldier of the Islamic State" who acted in response to calls to target citizens of the coalition of states combatting the organisation.

The claim, issued via Aamaq and attributed to a "security source", is typical of how the Islamic State (IS) has declared itself responsible for previous attacks in Europe.

The brief claim did not name the attacker or shed any light on his fate. The IS usually names attackers in statements that it issues later in its own name, not in initial claims via Aamaq.

Rita Katz, director of monitoring firm SITE, pointed out in a Tweet this was "the first Aamaq claim for a attacker while still alive; attackers in #France #Russia #America #Germany, etc. all killed prior to claim."

Six of the fatalities from the attack have been identified as German nationals, police chief Holger Muench said.

Five bodies still not identified

Five of the bodies have not yet been identified. A 31-year-old Italian woman, who had lived in Berlin for some years, was missing after the attack, the Italian news agency Ansa reported. A woman from Israel is also unaccounted for, according to Israeli media.

Among the dead was a Polish national who was a passenger in the truck and found shot dead at the scene. The murder weapon had not been recovered, said Interior Minister Thomas de Maiziere, who earlier confirmed that the incident had been an intentional attack.

The Polish man was apparently alive at the time of the attack, Germany's tabloid Bild reported in its online edition. Investigators spoke of potential evidence of a struggle before the lorry ploughed into the crowded market. He was found dead in the truck.

Germany's top prosecutor Peter Frank said that the method used in the attack was reminiscent of the truck attack in Nice, which left 86 people dead in July. He added that it was the "modus operandi" used by Islamist extremists.

Should it be confirmed, Monday's attack would be the first big Islamist attack in Germany. The IS has been linked to three terrorist attacks on German soil this year.

The Christmas market carnage comes less than six months after two terrorist attacks claimed by IS were carried out by people registered as asylum seekers in the country.

The attacks have led large swathes of the public to doubt Chancellor Angela Merkel's (photo) decision to keep German borders open to refugees last year.

Some 890,000 migrants entered the country in 2015, prompting a wave of support for the anti-immigration Alternative for Germany (AfD) party.

"Like millions of people in Germany, I am deeply saddened and horrified at what happened yesterday at Berlin's Breitscheidplatz," Merkel said in response to the attack, referring to the square around the landmark Kaiser Wilhelm Memorial Church, where the market is located. "We do not want to live in fear of evil."

At a memorial service at the church yesterday evening, officials called for a determined stance against hatred and division.

"The power of reconciliation is stronger than hatred," Bishop Markus Droege told the congregation. "We will not allow ourselves to be led into inhumanity by terror."

The service was attended by leading figures from the German government including President Joachim Gauck, Chancellor Angela Merkel and Berlin Mayor Michael Mueller, plus high-ranking officials from the Protestant and Catholic churches, but also leaders from Jewish, Orthodox and Muslim communities.

Earlier, Merkel, de Maiziere and Foreign Minister Frank-Walter Steinmeier all signed a condolence book at the church.

US President Barack Obama offered his country's full support in a telephone call with Merkel yesterday.

- dpa