A manhunt is under way across Europe after prosecutors identified a suspect in Monday's deadly lorry attack on a Berlin Christmas market.
German prosecutors named the man they are searching for as Anis Amri, 23, from Tunisia, warning he could be armed and dangerous.
His residence permit was found in the cab of the lorry.
The suspect had reportedly been under German surveillance earlier this year on suspicion of seeking to buy guns.
The German authorities are offering a reward of up to €100,000 (£84,000; $104,000) for information leading to his arrest.
Reports suggest he may have been injured in a struggle with the lorry driver, found murdered in the cab. The attack claimed 12 lives in all.
Police are searching a migrant shelter in the Emmerich area of North Rhine-Westphalia, western Germany, where the suspect's permit was issued.
Chancellor Angela Merkel has met her security cabinet to discuss the investigation into the attack.
In another development, the German cabinet approved plans agreed last month to allow more video surveillance of public places.
A police notice lists six different aliases used by Anis Amri, who at times tried to pass himself off as an Egyptian or Lebanese.
He is reported to have travelled to Italy in 2012 and then on to Germany in 2015 where he applied for asylum and was granted temporary leave to stay in April of this year.
Ralf Jaeger, the minister of interior of North Rhine-Westphalia, said on Wednesday that the claim for asylum had been rejected in June but the papers necessary for deportation had not been ready.
"Security agencies exchanged their findings and information about this person with the Joint Counter-Terrorism Centre in November 2016," the minister said.
Tunisia, Mr Jaeger said, had denied Anis Amri was its citizen, so the authorities had had to wait for temporary passport documentation from Tunisia. "The papers arrived today from Tunisia," Mr Jaeger added.
Judicial sources say the suspect was monitored in Berlin between March and September on suspicion of planning a robbery to pay for automatic weapons for use in an attack.
However, the surveillance was lifted for lack of evidence.
Sueddeutsche Zeitung reports that the suspect moved within the circle of an Islamist preacher, Ahmad Abdelazziz A, known as Abu Walaa, who was arrested in November.
History of crime
A brother of the suspect in Tunisia, Abdelkader Amri, told AFP news agency he could not believe his eyes when he saw his relative's face in the media.
"I'm in shock and can't believe it's him who committed this crime," he said, before adding: "If he's guilty, he deserves every condemnation."
The suspect has a history of crime:
- Anis Amri's father and security sources told a Tunisian radio station that after leaving Tunisia about seven years ago, he had served four years in an Italian prison over a fire at a school
- He was also sentenced to five years in prison in Tunisia in absentia, reportedly for aggravated theft with violence
An earlier suspect, a Pakistani asylum seeker, was freed from German custody on Tuesday, with officials saying there was no evidence to link him to the attack.
'Struggle with driver'
Some 49 people were also injured when the lorry was driven into crowds at the Breitscheidplatz Christmas market. So-called Islamic State said one of its militants carried out the attack but offered no evidence.
Polish citizen Lukasz Urban was found dead on the passenger seat with gunshot and stab wounds.
Investigators believe the lorry was hijacked on Monday afternoon as it stood in an industrial zone in north-western Berlin, Germany's Bild tabloid reports.
Mr Urban had stopped there after the delivery of Italian steel beams he was carrying was postponed until Tuesday.
GPS data from the vehicle reportedly shows it made small movements "as if someone was learning how to drive it" before leaving for the city at 19:40 (18:40 GMT), heading for the Christmas market near the Kurfuerstendamm, Berlin's main shopping street.
Lorry attack dead, missing and injured
Details of the casualties have begun to emerge:
- The only confirmed death is that of Polish lorry driver Lukasz Urban, who appears to have fought the attacker before dying of stab and gunshot wounds
- Italian expatriate Fabrizia di Lorenzo, 31, from Sulmona near L'Aquila, is feared dead. It is understood her phone and metro pass were found at the scene
- A woman from Neuss, near the west German city of Duesseldorf, is believed to be among the dead while her son, aged 40, is among the injured
- The German authorities have asked the family of Israeli woman Dalia Elyakim, missing since the attack, for DNA samples to help identify her; her husband Rami was seriously injured
- A Spanish student, 21-year-old Inaki Ellakuria, survived the attack with leg injuries. He has been tweeting (in Spanish) about his experiences
There appears to be evidence that, despite being stabbed, Mr Urban wrestled his hijacker for the steering wheel.
The post-mortem examination suggests that Mr Urban survived up until the attack and was shot dead when the truck came to a halt. No gun has been recovered.
Police say they are acting on hundreds of tips from the public and are examining DNA traces from the cab of the truck.
The IS group claimed the attack through its self-styled news agency, saying it was "in response to calls to target nationals of the coalition countries".
Prosecutor Peter Frank told reporters that the style of attack and the choice of target suggested Islamic extremism.