Germany on Saturday hunted for possible accomplices of Anis Amri, the suspected Berlin truck attacker who was gunned down by Italian police, as Tunisia announced it had arrested his nephew.
Tunisia's interior ministry said the nephew and two other suspected Islamist militants, aged between 18 and 27, were detained on Friday and were members of a "terrorist cell" connected to Tunisian-born Amri.
It made no direct link between the trio and the Berlin attack on Monday, when Amri is believed to have hijacked a truck and used it to mow down revellers at a Christmas market, killing 12 people.
Amri, 24, then went on the run and was the focus of a frantic four-day manhunt, before being shot dead by police in Milan after opening fire first.
The Berlin rampage was claimed by the Islamic State (IS) militant group, which released a video Friday in which Amri is shown pledging allegiance to IS chief Abu Bakr al-Baghdadi.
The Tunisian interior ministry said in a statement that Amri had sent money to his nephew so he could join him in Germany and had allegedly urged him "to pledge allegiance to Daesh (IS)".
The unnamed nephew also claimed that his uncle was the leader of an Islamist militant group based in Germany and known as the Abu al-Walaa brigade, it added.
The arrests come as German authorities are racing to find out whether Amri had help from accomplices before or after the attack.
"It is very important for us to determine whether there was a network of accomplices... in the preparation or the execution of the attack, or the flight of the suspect," federal prosecutor Peter Frank said Friday.
Seven of the victims killed in the attack were German nationals, a federal police spokeswoman told AFP. The other five came from the Czech Republic, Italy, Israel, Poland and Ukraine.
The fact that Amri was able to travel to Italy unhindered despite a Europe-wide arrest warrant has raised uncomfortable questions for intelligence agencies.
German security services have also faced criticism for not keeping better tabs on Amri before the Berlin carnage, even though he was a known criminal with links to the Islamist scene.
But Interior Minister Thomas de Maiziere denied there had been a blanket security failure.
It "is impossible to monitor every person suspected of posing a threat around the clock," he told the newspaper Bild am Sonntag.
Chancellor Angela Merkel has pledged a "comprehensive" analysis of how Amri was able to slip through the net and vowed to speed up the deportation of rejected asylum seekers like him.
The fugitive was killed after firing at two officers who had stopped him for a routine identity check Friday near Milan's Sesto San Giovanni railway station.
Media reports said a train ticket found in Amri's backpack suggested he had boarded a train in Chambery, southeastern France, and passed through Turin before arriving in Milan.
Milan police said Amri had a few hundred euros on him but no telephone.
Amri left Tunisia for Italy in 2011. He spent four years in prison there for starting a fire in a refugee centre, during which time he was apparently radicalised.
After serving his sentence he made his way to Germany in 2015, taking advantage of Europe's Schengen system of open borders -- as he did on his return to Italy this week.
German security agencies began monitoring Amri in March, suspecting he was planning break-ins to raise cash for automatic weapons to carry out an attack.
But the surveillance was stopped in September because Amri was seen primarily as a small-time drug dealer.
In a separate case, police said Saturday they had released two Kosovo-born brothers suspected of planning to attack a shopping centre in western Germany.
With the country on high alert, their arrests on Friday had made global headlines.
As Germany celebrated Christmas Eve meanwhile, locals and tourists in Berlin visited the Christmas market targeted in the truck assault, and many took a moment to quietly light a candle or lay flowers for the victims.
"It's really nice there are so many people here and it's still open," said Marianne Weile, 56, from Copenhagen.
"So even though you are really sad about what happened you can still keep Christmas. It's not like this crazy guy ruined it for everybody."