— -- Tunisian authorities have arrested three men in connection with this week’s terror attack at a Christmas market in Berlin that killed 12 and injured dozens, the country’s interior ministry said in a statement on its website.
The nephew, who was not named, admitted to using an encrypted chat application to communicate with his uncle, the ministry said in its statement.
The suspected Berlin attacker allegedly encouraged his nephew -- the son of his sister -- to adopt jihadist ideologies and urged him to pledge allegiance to the ISIS terror group, according to the ministry. He even went so far as to send money so that the nephew could travel to Germany and join a jihadist group.
"As he was interrogated, he confessed that he communicates with his uncle through the application Telegram to evade security surveillance using its encryption and secrecy," the statement said.
Meanwhile, Spanish authorities are looking into Amri’s internet activity. Investigators there are probing a possible communication between the Berlin attacker and a Spanish resident on Dec. 19, Spanish Interior Minister Juan Ignacio Zoido told a local radio station.
The identities of the other two men arrested are not known except that all three – whom the ministry said comprised a terrorist cell – are between ages 18 to 27.
Meanwhile, authorities are confirming new details linking Amri – a Tunisian national – to the attack on Monday.
Berlin police spokesman Winfried Wenzel confirmed to ABC News on Saturday that Amri’s mobile phone, wallet and ID were found inside the cab of the truck that was used to plow through unsuspecting crowds at the Christmas market.
The truck was stolen in Poland from a building site, and its driver, a Polish citizen, was found dead with gunshot wounds in the back of the vehicle.
The spokesman said authorities believe a violent struggle took place inside the cab at some point around the time of the attack.
In the wake of the attack, German Chancellor Angela Merkel phoned Tunisian president Beji Caid Essebsi to say that Germany will accelerate its deportations of Tunisian nationals "who have no right of abode in Germany."
Authorities are continuing to piece together Amri’s exact movements following the Monday attack..
He is believed to have traveled through France before arriving on a train at Milan’s central railway station at approximately 1 a.m. local time on Friday morning, according to a police spokesman in the Italian city.
Approximately two hours later, Amri was approached by two young police officers who wished to conduct a routine identity check. The officers were unaware he was the man at the center of the continentwide manhunt, police officials said.
"He was a man from northern Africa, like there are many in the Milan area, and ours was a routine check that was carried out by two young and good police officers,” said Antonio de Iesu, the head of Milan police, in a press conference on Friday.
Though Amri appeared initially to be calm while emptying his pockets and satchel, he unexpectedly drew a weapon and shot one officer before fleeing behind a nearby car, said Roberto Guida, head of Sesto San Giovanni police in suburban Milan.
Another officer flanked the assailant and shot him dead, police said.
The attack on Monday was reminiscent of an attack in Nice, France this past summer. In both cases the perpetrator used a truck to plow through assembled, unsuspecting crowds.
Since at least the summer of 2014, ISIS has been calling on its followers to use vehicles in attacks.
ABC News' Matthew McGarry contributed to this report.