The news comes after a man arrested following Monday’s incident was released, German prosecutors have said.
A Pakistani asylum seeker was arrested in the aftermath of the attack but denied any involvement, and police in Germany have admitted the person behind it may still be armed and at large.
It is understood the man was released because there was not enough evidence to link him to the attack and seek a formal arrest warrant to keep him in custody.
It came after federal public prosecutor Peter Frank said the “modus operandi” of the attack had echoes of July’s atrocity in Nice, in which 86 people died, and could have been the work of Islamic extremist groups, with the target of the attack “highly symbolic”.
But he told a press conference it was unclear if the attacker had an Islamist background, adding: “For now we don’t know whether there was one attacker or several attackers. We also don’t know whether they had support...
“We have to think that the person who was arrested yesterday, a man of Pakistani nationality, we have to be open to the idea that he could possibly not have been the attacker.”
While the attack at the heart of the German capital is being treated as terrorism, no organisation has come forward to claim responsibility, Mr Frank said.
Eleven people were killed when the articulated lorry careered through huts and stalls at the Christmas market near Kaiser Wilhelm Memorial Church, along with a Polish man found shot dead inside the lorry’s cab.
Following the incident, police arrested a 23-year-old Pakistani man who arrived in Germany on December 31 last year. But Berlin’s police chief Klaus Kandt later said officials were unsure whether they have detained the right suspect.
Holger Munch, head of the federal criminal police office, said the attack marked the realisation of a threat authorities were already aware of, adding that the country is now on a state of “high alert”.
German chancellor Angela Merkel and senior officials visited the scene of the attack on Tuesday, laying white roses among candles at a makeshift shrine to the dead and injured.
Earlier Mrs Merkel said: “Millions of people, including myself, are asking ourselves, how can you live with the fact that, while celebrating the festive season where we want to celebrate life, somebody has come along and took so many lives? I only know that we do not want, and we cannot live with it.
“We do not allow ourselves to be paralysed by terror. Although this might be difficult in these hours, but we will find a strength to continue living life as we want to live it in Germany, in freedom and openness and together.”
Prime Minister Theresa May paid her own tribute, saying events in Berlin had “shocked us all” as she offered condolences to those affected.
The attack has led to heightened security concerns in the UK, though a Number 10 spokesman said there were “no plans” to change the UK’s security level, which currently stands at “severe” - meaning a terror attack is highly likely.
But police, including Scotland Yard, are reviewing preparations already in place to protect public events over the Christmas and New Year period.
Greater Manchester Police also said it had strengthened its presence at Christmas markets, which have almost 350 stalls spread across 10 sites in the city.
Meanwhile, increased security measures will see some of London’s most famous streets around Buckingham Palace face closures for the next three months.
The restrictions have been planned for some time, but have been brought forward in light of the Berlin attack.
From Wednesday, Constitution Hill, the Queen Victoria Memorial, Spur Road, Link Road and The Mall - up to the junction with Marlborough Road - will be closed at specific times on the days of Changing the Guard.
Additional barriers will also be in place to maintain security for the guard movements, Scotland Yard said.
The closures follows a request from the Metropolitan Police as part of ongoing security measures.
The force highlighted to the The Royal Parks that due to the event’s high profile with a substantial military presence and attracting large crowds, the closures were a necessary precaution.
Met Commander Simon Bray, responsible for security, said: “The Met undertakes a range of different activities including strengthening security and high-visibility policing as part of a counter-terrorist strategy, and it will continue to take whatever action it believes is necessary to protect and reassure the public.
“Police continue to work in partnership to minimise disruption, but its priority is to ensure the safety and security of those who live, work and visit London.”
On the days of Changing the Guard road closures will be in place from around 10.45am to 12.30pm.
The threat to the UK from international terrorism remains severe, meaning an attack is highly likely.
The public is urged to be alert but not alarmed, and report anything suspicious to the Anti-Terrorist Hotline on 0800 789 321, but dial 999 in an emergency.