A spokesman for the German chief federal prosecutor on Thursday denied a media report saying that there had been four arrests of people who had contact with the Tunisian suspect in the Berlin Christmas market attack.
"No, that's not the case," the spokesman said when asked about the report in Bild.
"We do not know of any arrest," he added.
German authorities are under fire after it emerged that the prime suspect in Berlin's deadly truck attack, a rejected Tunisian asylum seeker, was known as potentially dangerous.
German prosecutors have issued a Europe-wide wanted notice for 24-year-old Anis Amri, offering a 100,000-euro (A$144,200) reward for information leading to his arrest and warning he "could be violent and armed".
Asylum office papers believed to belong to Amri, alleged to have links to the radical Islamist scene, were found in the cab of the 40-tonne lorry that rammed through a crowded Christmas market in Berlin on Monday, killing 11.
The twelfth victim, the hijacked truck's Polish driver, was found shot in the cab.
Police Wednesday searched a refugee centre in Emmerich, western Germany, where Amri stayed a few months ago, as well as two apartments in Berlin, the media reported.
But as the Europe-wide manhunt intensified, questions were also raised about how the suspect had been able to avoid arrest and deportation despite being on the radar of several security agencies.
"The authorities had him in their crosshairs and he still managed to vanish," said Der Spiegel weekly on its website.
The Sueddeutsche Zeitung criticised police for wasting time focusing on a Pakistani suspect immediately after the truck assault, in what turned out to be a false lead.
The wanted poster issued by German federal police on Wednesday, Dec. 21, 2016 shows 24-year-old Tunisian Anis Amri. Source: German Federal Police
"It took a while before the federal police turned to Amri as a suspect," it said.
The attack, Germany's deadliest in recent years, has been claimed by the Islamic State group.
Twenty-four people remain in hospital, 14 of whom were seriously injured.
Germany has boosted security measures following the carnage, beefing up the police presence at train stations, airports and at its borders with Poland and France.
'Planning an attack'
In a revelation likely to stoke public anger, German officials said they had already been investigating Amri, suspecting he was planning an attack.
The interior minister of North Rhine-Westphalia state, Ralf Jaeger, said counter-terrorism officials had exchanged information about Amri, most recently in November, and a probe had been launched suspecting he was preparing "a serious act of violence against the state".
Berlin prosecutors said separately that Amri had been suspected of planning a burglary to raise cash to buy automatic weapons, "possibly to carry out an attack".
But after keeping tabs on him from March until September this year they failed to find evidence of the plot, learning only that Amri was a small-time drug dealer, and the surveillance was stopped.
, Amri had researched online how to build explosives and had communicated at least once with Islamic State.
The 24-year-old had communicated with the extremist organisation at least once and was also on a US no-fly list, the newspaper said, citing a US official who spoke on condition of anonymity.
Amri, who has several aliases and was facing deportation, is believed to have fled the scene of Monday's attack, which left 12 people dead and 48 injured, including the truck's Polish driver, who was found shot, stabbed and bashed in the cabin.
Identity documents belonging to Amri were found in the truck after the attack, which has left Germany's capital badly shaken.
Amri had been under surveillance between March and September, and was suspected of planning to steal money in order to buy an automatic weapon "possibly to later commit an attack with future accomplices," the Berlin investigating authorities said.
The surveillance did not produce the necessary evidence to bring charges against him.
Fourteen of those injured in the carnage remain in a life-threatening condition.
Meanwhile police raided a refugee home in North Rhine Westphalia on Thursday as the Europe-wide hunt continued for the Tunisian.
About 100 officials, including special units, were involved in the operation in the city of Emmerich, which ended after roughly one hour.
Police did not disclose the result of the search of the refugee home and provided no further comments.
Meanwhile Danish police say they have searched a port and a ferry in northern Denmark after a tip off that 24-year-old Anis Amri had been sighted there, but the search did not yield any result.
"Our assessment this morning is that nothing suggests he is or has been in Grenaa," police spokesman Klaus Arboe Rasmussen told reporters.
Police acted on information received late Wednesday, he said.
Police deployed a helicopter as well as officers, and dog patrols. Rasmussen said police patrols would remain in the area as the Europe-wide search continued for Amri.
Family 'in shock'
In Tunisia, Amri's family expressed disbelief on hearing that Amri was wanted across Europe.
"I'm in shock, and can't believe it's him who committed this crime," his brother Abdelkader Amri told AFP.
But "if he's guilty, he deserves every condemnation. We reject terrorism and terrorists -- we have no dealings with terrorists."
Amri left Tunisia after the 2011 revolution and lived in Italy for three years, a Tunisian security source told AFP. Italian media said he served time in prison there for setting fire to a school.
He arrived in Germany in July 2015 but his application for asylum was rejected this June.
His deportation, however, got caught up in red tape with Tunisia, which long denied he was a citizen.
Merkel under pressure
The apparent security failings in the case triggered fresh criticism of Chancellor Angela Merkel's liberal refugee policy, which has seen over a million people arrive since last year.
The record influx has fuelled support for the nationalist anti-migrant AfD party, which has accused Merkel of endangering the country.
But even within the chancellor's own CDU party voices of dissent are growing louder.
"Nationwide, there are a large number of refugees about whom we don't know where they're from or what their names are. And that's a potential major security issue," said CDU member Klaus Bouillon, the interior minister of Saarland state.
Germany had until now been spared the devastating jihadist carnage that has struck neighbouring France and Belgium.
But it has suffered a spate of smaller attacks, including two attacks in July that left 15 people injured. Both were committed by asylum seekers and claimed by IS.
The Berlin Christmas market carnage evoked memories of the July 14 truck assault in the French Riviera city of Nice, where 86 people were killed by a Tunisian IS-sympathiser.
Populists across Europe have seized on the truck attack in Berlin as a way to criticise Germany's immigration policy but key players have held back on jumping to conclusions as the investigation continues.
Former UK Independence Party (UKIP) leader Nigel Farage, a key ally of US President-elect Donald Trump in Europe, said the attack which killed 12 people was "no surprise" and would be part of Merkel's "legacy".
"Merkel has directly caused a whole number of social and terrorist problems in Germany, it's about time we confronted that truth," he told LBC radio on Tuesday.
UKIP donor Arron Banks, who was also a key funder behind the Brexit campaign, tweeted that Merkel "might as well have" been driving the truck herself.
Just hours after Monday's attack, far-right Dutch lawmaker Geert Wilders sharply blamed European leaders for admitting asylum-seekers into Europe.
"Merkel, (Dutch Prime Minister Mark) Rutte and all the other cowardly government leaders have allowed in Islamic terror and an asylum tsunami with their open borders policy," he tweeted on Tuesday.
Wilders, who heads the anti-Islam Freedom Party (PVV), also tweeted a photo-shopped picture of Merkel with her hands, face and jacket spattered in blood.
The image was not accompanied by any words, but implied she had blood on her hands for the attack.
Slovak Prime Minister Robert Fico on Tuesday said the Berlin attack had been "the last drop in the cup of patience" in Europe's migration crisis.
