Isis has claimed responsibility for the lorry attack on a crowded Christmas market in Berlin.

Through its Amaq news agency, the jihadi group has claimed the attacker is a "soldier of the Islamic State".

The phrase matches that used to claim previous lone wolf attacks, such as those in Orlando and Wurzburg.

The statement also said the attacker "carried out the attack in response to calls to target nationals of countries in the international coalition".

It did not name the attacker.

Berlin Christmas market lorry attack Show all 18 1 /18 Berlin Christmas market lorry attack Berlin Christmas market lorry attack Several people have been killed after a lorry drove into crowds at a Christmas market in Berlin REUTERS/Fabrizio Bensch Berlin Christmas market lorry attack 'At least nine' people have been killed and more than 50 injured. AP Berlin Christmas market lorry attack Emergency Services rush a Berlin market victim to an ambulance Associated Press Berlin Christmas market lorry attack Police cordoned off the square at Kaiser Wilhelm Memorial Church following the incident REUTERS Berlin Christmas market lorry attack Rescue workers inspect the lorry that crashed into a Christmas market close to the Kaiser Wilhelm memorial church in Berlin EPA Berlin Christmas market lorry attack Emergency crews inspect the lorry that ploughed into a Berlin Christmas market, killing at least nine people AFP Berlin Christmas market lorry attack Fire crews attend the scene of the attack AFP/Getty Berlin Christmas market lorry attack Armed police secure the site of a lorry attack at a Christmas market in Berlin REUTERS Berlin Christmas market lorry attack Crushed debris is visible beneath the wheels of the vehicle REUTERS Berlin Christmas market lorry attack An injured man is pushed to an ambulance REUTERS Berlin Christmas market lorry attack Medics attend an injured person after the lorry attack which killed at least nine and injured more than 50 people AFP/Getty Berlin Christmas market lorry attack Firefighters examine the lorry which was rammed into a Berlin Christmas market REUTERS Berlin Christmas market lorry attack A person is carried into an ambulance REUTERS Berlin Christmas market lorry attack View of the lorry that crashed into a Christmas market in Berlin, killing at least nine and injuring at least 50 people AFP/Getty Berlin Christmas market lorry attack Rescue workers push a person on a stretcher to an ambulance Getty Berlin Christmas market lorry attack Firefighters assess the damage after the lorry rammed the Christmas market, killing 'at least nine', and injuring more than 50 people AP Berlin Christmas market lorry attack Firefighters stand beside a toppled Christmas tree at the site of the suspected terrorist attack in a Berlin Christmas market AP Berlin Christmas market lorry attack Damaged stalls at the scene of the incident at a Berlin Christmas market where at least nine people have been killed EPA

Speaking after the Isis claim, German Interior Minister Thomas de Maiziere said investigators are following several leads.

"We just heard about the supposed claim of responsibility by this so-called Islamic State that is in fact a gang of terrorists," Mr de Maiziere told ARD broadcaster.

"There are several leads that investigators are following now," the minister added.

Mr de Maiziere added that "nobody will rest until the perpetrator or the perpetrators are caught".

Merkel on Berlin attack: 'We must assume it was terrorism'

Earlier on Tuesday, German authorities released a Pakistani asylum-seeker who was suspected of driving a truck into the market, killing 12 people and injuring 48.

The interior minister said the perpetrator of the attack is probably still on the run.

He said the man arrested earlier was released due to lack of evidence.

Witnesses saw only one man flee from the truck after it rammed into the crowd at the Christmas market, smashing wooden stalls and traveling 60 to 80 meters (200 to 260 feet) before coming to a halt.

Six of those killed have been identified as Germans, and a man found shot and killed in the truck's passenger seat was Polish.

The other five people killed have not yet been identified. Twenty-five people remained in hospital, 14 with serious injuries.

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Chancellor Angela Merkel has insisted the attack cannot change Germans' way of life.

"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 before heading to the scene of the attack in downtown Berlin.

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

Ms Merkel, who has been criticised for allowing in huge numbers of migrants last year, addressed the possibility that an asylum-seeker was responsible for the carnage head-on.

"I know that it would be particularly hard for us all to bear if it were confirmed that a person committed this act who asked for protection and asylum in Germany," Ms Merkel said.