Fear and anger is growing in Germany over a lorry attack that killed 12 people after police were forced to release their only suspect, admitting the real culprit was still at large.

Isis claimed responsibility for the massacre that targeted Germans and tourists enjoying one of Berlin’s most popular Christmas market, calling the perpetrator was a “soldier of the Islamic State” obeying calls to attack members of the US-led coalition.

The group issued its propaganda statement hours after investigators maintained they could not confirm the atrocity was either a terror attack or motivated by Islamist extremism.

Thomas de Maizière, the interior minister, confirmed security services had received the claim on Tuesday evening but urged caution.

“We should let the security forces do their job,” he added. “Nobody will rest until the perpetrator or perpetrators are caught.”

Klaus Kandt, the president of Berlin Police, admitted that the culprit remained on the loose and could pose a further threat.

“It is the case that we may have a dangerous criminal in the area and that of course makes the public nervous,” he said.

“We are boosting security measures. Heightened vigilance is also needed at the moment.”

A suspect identified by local media as a 23-year-old Pakistani asylum seeker was arrested near the scene shortly after Monday night’s attack, with hundreds of armed police launching a dawn raid on the migrant accommodation centre where he was thought to be registered.

But he denied any involvement and was released 24 hours later after investigators failed to uncover evidence needed to extend his detention under German law.

The federal public prosecutor’s office said investigations had not established any links to the crime, and that eyewitnesses whose statements were used for the suspect’s arrest had lost track of the driver after he fled the vehicle.

“Criminal investigations carried out so far have not been able to prove the accused was present inside the lorry’s cab during the incident,” a spokesperson said.

The attacker is believed to have shot the Scania lorry’s Polish driver dead before hijacking it, driving it into the Christmas market and fleeing on foot, leaving more than 60 victims strewn among destroyed huts and stalls.

Confusion reigned as Angela Merkel joined hundreds of mourners at a memorial service at the Kaiser Wilhelm Memorial Church, which towers over the market.

Hundreds more were unable to enter the packed service, gathering inside the deserted Christmas market instead and holding makeshift vigils under the watch of heavily armed police in Breitscheidplatz.

Many openly wept as they were hugged by friends and loved ones, laying down candles and flowers or simply standing in silence to listen to the prayers and music broadcast from inside the church.

Berliners, tourists, Muslims and Jews could all be seen among the crowds braving the freezing cold in a show of defiance against the terror wreaked less than 24 hours before.

Muhammad Asif Sadiq attended the vigil with a group of Ahmadiyya Muslims giving out T-shirts reading “love for all, hate for none” in German.

“We’re here tonight to show our face against terrorism,” he said. “Muslims who live here fight for peace, fight for loyalty and they love their country. We are here as citizens of Berlin and we love living here.”

Mr Sadiq, who is of Pakistani origin, said people had “started looking at foreigners differently” over recent years in Germany but was confident that Berlin would rise above growing anti-migrant sentiment.

“Changing ourselves is not the answer – we have to change the terrorists to we are strong,” he said, adding a message for the attacker: “If he does not like the way people live here, just leave the country.”

Zeynep Cetinkaya, a German woman of Turkish heritage, described the panicked search to check on her friends and family as news of the attack spread, with several victims still unidentified.

“Just one day after what happened, people are not hiding at home, they are here in the same place to show their strength,” she said.

One of her friends, Sami Atris, said he was among several members of his mosque attending the vigil, adding: “We are Muslim people but we are also German people and this was an attack on us Germans. We are here to show we won’t let anyone divide us and we will stand here, together in love and peace.”

Yasin Uzuner, who was putting down candles with his wife and two young children in the deserted Christmas market, said the attack struck Berlin particularly hard by targeting the festive period.

But said he still felt safe in the German capital. “We will come back here,” he added, calling demands for Germany to shut its borders “rubbish”.

Angelina Ferrera and her mother were standing with a group of people holding candles opposite the church as hymns rang out.

The 30-year-old vowed that Berlin would not be “polarised” by the attack, adding: “It’s important to be here with our friends, with our community. This person tried to divide us and they will not succeed.”

Her mother, Karin Muolo, recalled life under the Communist DDR and said Berlin would not lose its spirit of freedom.

Asked whether political opponents were right to blame Ms Merkel for terror attacks because of her refugee policy, she called the idea “totally false”.

Germany’s anti-immigration Alternative für Deutschland (AfD) party swiftly moved to capitalise on the massacre, blaming the Chancellor’s decision to open borders to asylum seekers during the height of the crisis in 2015.

The lorry attack and a previous Isis suicide bombing and axe attack carried out by asylum seekers are expected to damage Ms Merkel’s bid to be re-elected for a fourth term as Chancellor in next year’s federal elections, amid growing anti-migrant sentiment and fear of further atrocities.

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

Those hoping for an apology were disappointed as she made a defiant speech. “We cannot allow ourselves to be paralysed by fear,” she said, before laying a rose among tributes by the scene of the massacre.