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The Islamic State group on Tuesday claimed responsibility for a truck rampage through a Berlin Christmas market that killed 12 people, as German police hunted for the attacker.

"A soldier of the Islamic State group carried out the Berlin operation in response to appeals to target citizens of coalition countries," the IS-linked Amaq news agency said, without identifying the perpetrator.

Germany is not involved in anti-IS combat operations, but has Tornado jets and a refueling plane stationed in Turkey in support of the coalition fighting militants in Syria.

It also has a frigate protecting a French aircraft carrier in the Mediterranean, among other assets.

The claim of responsibility for the attack came shortly after German prosecutors, saying they lacked evidence, released a Pakistani asylum seeker who was the sole suspect in the case.

It sparked fears that the killer was armed and at large.

"We can't rule out that the perpetrator is on the run," Interior Minister Thomas de Maiziere told broadcaster ZDF, adding he was confident there would be "progress" in the inquiry.

The Pakistani was arrested late on Monday after he was reportedly seen jumping out of the truck and fleeing the scene.

Federal prosecutors said they had found nothing to link the suspect to Germany's deadliest attack in recent memory.

"The forensic tests carried out so far did not provide evidence of the accused's presence during the crimes in the cab of the lorry," the prosecutor's office said.

A soldier of the Islamic State carried out the Berlin operation in response to appeals to target citizens of coalition countries. - Amaq, IS-linked news' agency

But officials had expressed growing doubts over whether they had the right suspect in custody.

Berlin's police chief Klaus Kandt earlier warned that "we may have a dangerous criminal in the area", and announced security would be boosted while urging "heightened vigilance".

As attention switched to the man hunt, investigators asked the public to send them any photos and video footage.

Twelve people were killed when the truck tore through the crowd, smashing wooden stalls and crushing victims, in scenes reminiscent of July's deadly attack in the French Riviera city of Nice.

Another 48 people were injured, 24 of whom were released from hospital by late on Tuesday.

Possible 'terrorist' attack

Chancellor Angela Merkel - who visited the scene of the carnage for a minute's silence and then joined a memorial service in the adjacent Kaiser Wilhelm Memorial Church - labelled the deadly rampage a likely "terrorist" attack.

"Twelve people who were still among us yesterday, who were looking forward to Christmas, who had plans for the holidays, aren't among us anymore," she said in an emotional, nationally televised statement.

"A gruesome and ultimately incomprehensible act has robbed them of their lives."

Merkel visited the scene of the carnage for a minute's silence [Getty]

The government declared that the city's 60-odd Christmas markets - after a one-day voluntary stoppage out of respect for the victims - should continue because "we must not let our free way of life be taken from us".

Europe has been on high alert for most of 2016, with bloody jihadist attacks striking Paris and Brussels. 

Germany also suffered two attacks in July in the southern state of Bavaria committed by asylum seekers and claimed by IS. 

An axe rampage by an Afghan or Pakistani man on a train wounded five people, and a suicide bombing by Syrian asylum seeker left 15 people injured six days later.

The arrival of 890,000 refugees last year has polarised Germany, with critics calling the influx a serious security threat.

Merkel said earlier that if the attacker turned out to be an asylum seeker, this would be "particularly sickening in relation to the many, many Germans who are involved every day in helping refugees".