The Islamic State released a video today purportedly showing the Berlin attack suspect vowing to take revenge for Muslims killed in Western airstrikes.
In the video, released by Islamic State's semi-official Amaq agency, an Arabic-speaking man pledges allegiance to Islamic State leader Abu Bakr al-Baghdadi.
He urges Muslims in Europe to carry out attacks.
"My message to the crusaders: We've come to slaughter you, pigs. The blood of monotheists (Muslims) will not go in waste," he says in the video.
Amaq gives the speaker the jihadist nom de guerre Abu Bara al-Tunisia, meaning he is a Tunisian native.
Earlier today, the ANSA news agency and Italy's Corriere della Sera newspaper reported that the Berlin truck attack suspect, Anis Amri, was shot dead in Milan.
There has been a four-day Europe-wide manhunt for Amri, a 24-year-old Tunisian national who is believed to have driven the large truck laden with steel into a Berlin Christmas market late Monday, killing 12 people and injuring 48.
Amri reportedly spent several years in Italy before entering Germany in July 2015.
According to ANSA, Amri was stopped overnight to Friday as part of a routine police control. When asked to show his documents, he pulled out a gun and shot a police officer in the shoulder. Police then returned fire and shot him dead.
Italian Interior Minister Marco Minniti was due to address reporters in Rome shortly.
"The investigations are ongoing - we are in contact with the Italian security authorities," a spokesperson for the German federal prosecutor's office told dpa without giving further details.
German authorities had believed that Amri was unlikely to have fled beyond Berlin after the attack, and carried out several raids across the city.
Yesterday and today, police searched a mosque in Berlin's Moabit district where Amri was reportedly sighted several days before and immediately after the attack.
Amri arrived in Italy in February 2011, among thousands of migrants from Tunisia who crossed the Mediterranean in the wake of the Arab Spring, the ANSA news agency reported earlier. He spent several months in a youth centre near the Sicilian city of Catania.
On October 23, 2011, Amri was arrested on suspicion of arson, assault, intimidation and embezzlement, and was later sentenced to four years in prison, during which he was detained in six different Sicilian facilities.
As a detainee, he was reported 12 times for violent or unruly behaviour, which was the cause of his frequent prison transfers, but did not display any signs of radicalisation, according to judicial documents cited by ANSA.
On May 18, 2015, Amri was released from Palermo's Ucciardone prison, but remained under custody in a migrant detention centre after being issued with a repatriation order, ANSA said.
The order could not be executed because Tunisian authorities did not respond in time to requests for his identification. He was eventually let go and given orders to leave Italy of his own accord.
Two months later he entered Germany via the south-western city of Freiburg, which is close to the Swiss and French borders, according to local authorities.