Gordon Corera
Security correspondent, BBC News

Image source, EPA

No-one should be surprised that a Christmas market was attacked or even the way the attack was carried out. 

But the challenges in preventing such low-tech attacks are complex. A decade ago those working with al-Qaeda tended to plan more complex attacks involving explosives. This often required international travel and training as well as communication and such plots took time to develop.  

This all provided potential opportunities for intelligence agencies to learn about the plans and interdict them. 

But if an individual is inspired by so-called Islamic State but not in touch with them and acts either alone or in a small cell, then it can be harder to spot them. By the time they hijack a lorry just before an attack, the worst case is that it is more of a case of protecting possible sites rather than spotting them.

There may be questions though as to whether enough was done in Berlin given that this threat was known about. 

The US state department issued a warning in late November telling American citizens to exercise caution at "holiday festivals, events and outdoor markets". 

Increased security was put in place at some Christmas markets – such as the more famous one at Strasbourg with checks on people and restrictions on vehicle movements.  

But one risk is that if all markets are not secured to the same standard, it might simply divert an attacker to a less well defended target. 

German officials have sought to defend their preparations, especially since there do not appear to have been obstacles capable of stopping a lorry in Berlin.

Read more from Gordon

A simple message from Berlin's police tonight.

Earlier we showed you Brandenburg Gate was lit up in the colours of the German national flag.

The famous landmark has also been lit in the colours of the flag of Berlin - red, white and red stripes with a black bear in the middle.

US President Barack Obama on Monday night spoke on the phone with German Chancellor Angela Merkel to offer condolences, the White House says in a statement released on Tuesday, Reuters reports. 

It says Mr Obama described the lorry incident as a "horrific apparent terrorist attack", adding that the US stood ready to provide assistance to German investigators. 

Mr Obama stressed "that no attack could sway our determination - and that of our German allies - to defeat terrorism in all of its forms," the statement says. 

Image source, Reuters

Der Spiegel, external (in German) says it has been told that Polish lorry driver Lukasz Urban died from a single shot to the head from a small-calibre gun and was already dead when the attacker drove the vehicle at Christmas market crowds.

The attacker reportedly also drove around the market before aiming the vehicle at people, perhaps in order to get a better run-up, Spiegel reports.

The attacker got out of the lorry and was followed by a witness who is then said to have lost him in the Tiergarten park.

A Pakistani man was later arrested at the Victory Monument on the basis of the description of the attacker given to police by the witness, Spiegel says.

Berlin's famous Brandenburg Gate has been lit up in black, red and yellow - Germany's national flag colours.

Austria has arrested a 25-year-old asylum seeker from Morocco on suspicion of planning an attack during the holiday season in the city of Salzburg, prosecutors say. 

Police were acting on information that a group of men had discussed such an attack and the Moroccan was the main suspect, Reuters reports.

Although a search of his accommodation in a centre for asylum seekers in the town of Fuschl am See, where the man was living, found "no materials clearly required for the execution of an attack", a police spokesman said it could not be ruled out that he was planning an attack.

Six of the 12 people killed in the attacks have been identified, says Holger Munch, the head of Germany's federal criminal police office. 

He says all six are German nationals, adding that the identities of the other six are yet to be established.

Berlin police say that 24 people injured in Monday's attack have now left hospital to reunite with their relatives.

In all, 12 people were killed and 48 wounded when the lorry ploughed into Berlin's Christmas market.

Germany's interior minister earlier said that 18 of the injured were in a serious condition.

Image source, ap

More from the Polish owner of the lorry involved in Monday's attack (see our previous entry at 15:27).

Ariel Zurawski has identified the man found dead in the vehicle's cabin as his cousin Lukasz Urban, Associated Press reports. 

He is reported to be 37 year old from western Poland, near the German border. 

BBC Radio 5 live

A Christmas market trader who witnessed the lorry attack says people have to still “live Christmas as it’s supposed to be”.

Sofiane, 29, said he was “supposed to be one of the victims” as his stall was originally meant to be on the side that got hit. Its position was changed “at the last minute”.

He told BBC Radio 5 live's Nick Garnett that his “thoughts” were with the victims' families and that people should respond by "living [their] lives".

As darkness falls, BBC's Nick Garnett tweets, Berliners have been lighting candles to remember the victims of Monday's attack.

The World at One
BBC Radio 4

The right-wing German party Alternatives Fuer Deutschland has blamed Chancellor Merkel for the attack on the Berlin market.

They have criticised Mrs Merkel's decision to allow around a million migrants into Germany over the past two years.

Beatrix von Storch, a German MEP, and AfD's vice-chair, tells BBC's The World at One programme that "it is not possible to let in so many refugees" and "as far we know the terrorist was one of them".

Read more: What does Alternative for Germany (AfD) want?

Berlin police chief Klaus Kandt says police are examining a mobile phone they seized during a night-time search at Berlin’s now-defunct Tempelhof airport, where asylum seekers are living, Focus, external magazine reports.

Referring to the suspect now being questioned by police, Mr Kandt said “I’m pretty sure we found the correct place – that is, where he spent the night”.

Police say the suspect had previously come to their attention, but he was not listed in connection with weapons or possible links to Islamists.

Image source, AP

The Polish owner of the lorry has said he confirmed the identity of the man found dead in the vehicle after police had shown him a photograph. 

Ariel Zurawski told Polish TV via Reuters that the man, who he says was his cousin, was "stabbed to death and shot". 

"Stab wounds were clearly visible on the photo, it was a photo showing the face of my cousin, it was really clear that he had been fighting. His face was all swollen and bloodied. 

"The last contact we had with the driver was at 15:00 (on Monday) when his wife called him," Mr Zurawski said.

German police earlier said the man had been shot.

Image source, EPA

Earlier on Monday, Chancellor Angela Merkel held a crisis meeting with top security officials and cabinet ministers to discuss how to respond to the attack.

Berlin police thank for all the photos and videos sent to the information portal of the federal criminal authorities, saying this "helps enormously" in the investigation.

Image source, Getty Images

A refugee living in makeshift accommodation in Berlin has said he is worried how the German people will view migrants in light of the lorry attack.

Special forces officers searched a hangar at the former Tempelhof airport, which is home to about 2,000 migrants, following the Monday's attack.

Ibrahim Sufi, a 26-year-old Syrian living at the airport, told Reuters: "We are of course worried.

"We are worried about how the German public will view us after this terrorist attack.

"My message to the Germans is: 'Don't suspect everybody, don't generalise.'"

Berlin police tweet that "with deep sadness" officers observed a minute's silence to think of the victims of the attack.

Image source, Getty Images

Concrete barriers have been put up to protect shoppers at the Christmas market in Dresden.

BBC's Berlin correspondent Jenny Hill tweets that barriers are also being put up at other large Christmas markets.

UK Prime Minister Theresa May has offered her condolences to those affected by Monday's attack in Berlin. 

"We've seen very vivid images in our newspapers and on television and I think they've shocked us all," she told MPs in London.

"And I just wanted to express our condolences. I'm sure the condolences of all of us are with those who mourn and all those who've been affected and we hold them in our thoughts today."