A German minister has admitted security forces knew the suspected Berlin attacker was a terror threat but failed to detain or deport him before he ploughed a lorry into a Christmas market.

Ralf Jäger, the interior minister of North Rhine-Westphalia, told a press conference the Tunisian man had already been put under investigation over a previous attack plot but missing paperwork meant he could not be ejected from Germany.

Anis Amri, 24, was the subject of a meeting of its Joint Terror Protection Centre and federal and local government officials shared information as recently as last month, with the police warning he posed a threat.

Prosecutors are offering a €100,000 reward for information leading to his arrest, describing Amri as 5ft 10in tall and weighing just under 12 stone, with black hair and brown eyes.

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“If you see the person being sought, notify the police,” read an appeal. “Do not put yourself in danger, because the person could be violent and armed.”

Mr Jäger said a separate investigation was launched into plans for “a serious act of violence against the state” earlier this year but Amri could not be deported because of a bureaucratic dispute with Tunisia, which originally said he was not a citizen.

“The man could not be deported because he had no valid identification papers,” the minister added, saying Germany requested the necessary documents in August.

They arrived today – two days after the Berlin attack – and would have allowed authorities to carry out the deportation order issued after Amri’s asylum application was rejected in June.

A spokesperson for the North Rhine-Westphalia interior ministry told The Independent local police launched an investigation into the suspect over a separate attack plot earlier this year and handed their information to Germany’s Federal Criminal Police Office (BKA), which shut the investigation in September.

When asked why Amri was not arrested, he replied: “I don’t know, ask Berlin.” A spokesperson for the BKA said she could not comment on previous investigations but an anonymous source told Reuters there was insufficient evidence to proceed.

Prosecutors launched a probe into claims Amri was planning a break-in to finance buying automatic weapons for an attack, but surveillance that started in March failed to reveal evidence of a terror plot and was stopped six months later.

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

Amri's estranged father told a Tunisian radio station his son was born in 1992 and lived in the Oueslatia region,

He said Amri left his home country around seven years ago and had a lengthy criminal past, being jailed in Italy for setting fire to a school and previously sentenced in absentia to five years in prison for aggravated robbery in Oueslatia, Tunisia.

Mr Jäger said the man arrived in Germany in 2015 and went under “numerous” aliases – a technique previously used by terrorists including the Paris and Brussels attackers to throw authorities off their scent.

The suspect had been living in Berlin since February, having previously stayed areas including Kleve in North Rhine-Westphalia and the city of Freiburg, in Baden-Württemberg.

Amri’s identity was confirmed by prosecutors hours after he was named in German media reports after identification documents were found inside the lorry used in Monday night’s massacre.

At least 12 people were killed and dozens injured when it ploughed into crowds enjoying a popular Christmas market in central Berlin.

Stephan Mayer, a politician from the CSU party, said the new suspect had ties to a network of Islamic extremists, reported to include a hate preacher known as Abu Walaa, who was arrested as part of a cell of Isis supporters sending militants to Syria earlier this year.

Amri was also said to have followed an extremist preacher known as Boban S, who was arrested in Dortmund on suspicion of supporting Isis in November.

Tunisian officials said they would be working with the German government in the probe, which comes months after another Tunisian man who lived in France was shot dead after using a lorry to kill 86 people in Nice.

Anis Amri, the latest suspect in the Berlin lorry attack (Facebook)

Amri, who also claimed to be Egyptian and Lebanese while using fake passports and documents, was classified as a terror threat and put under increased surveillance before a court in Ravensburg issued an order for his deportation in June.

A Pakistani asylum seeker originally arrested on suspicion of being the attacker has been released after no evidence was found against him, leaving the attacker at large and possibly armed.

The German interior minister, Thomas de Maiziere, said a European arrest warrant was issued for Amri as the manhunt spread from Germany throughout the EU’s Schengen area amid warnings the suspect could pose a further threat.

A gun used to shoot the Polish driver of the hijacked lorry has not been found, with witnesses losing track of the attacker as he fled.

Isis claimed responsibility for the massacre, calling the perpetrator a “soldier of the Islamic State” who was obeying calls to attack supporters of the US-led coalition launching air strikes on its territories in Syria and Iraq.

Coming after two previous Isis terror attacks by asylum seekers earlier this year, the massacre has fuelled increasing anger against Angela Merkel’s government over its decision to open the borders to refugees last year, sparking the arrival of almost 90,000 asylum seekers.

She will face fierce opposition from the anti-immigration Alternative for Germany (AfD) party, whose leader claimed Ms Merkel’s bid for a fourth term in next year’s election was “finished” by the lorry attack.

The Chancellor was among hundreds of mourners who packed the Kaiser Wilhelm Memorial Church for a service next to the destroyed market on Tuesday evening and hundreds of people held an emotional vigil outside.