Three people including the nephew of the Berlin Christmas market attacker Anis Amri have been arrested in Tunisia.
Tunisia's Interior Ministry said Amri - who was shot dead on Friday - had sent his 18-year-old nephew Fedi money to join him in Europe.
Twelve people were killed and dozens more injured in the attack on Monday.
A video has emerged purportedly showing the suspect behind the Berlin Christmas market attack pledging allegiance to the so-called Islamic State.
Anis Amri was shot dead in Milan on Friday after being on the run since Monday's attack in Berlin, in which 12 people were killed and 48 injured.
ITV News Security Editor Rohit Kachroo said the video, recorded in north Berlin, provides powerful evidence.
He said: "When it was filmed is not clear, but the sentiment is emphatic.
"He pledges allegiance to the IS leader [Abu Bakr al-Baghdadi]. A video selfie, apparent proof he was inspired by the group."
The funeral for the lorry driver killed in the Berlin Christmas market attack has taken place in his home country of Poland.
Footage has emerged of the final moment before a truck ploughed into a crowd of people at a Christmas market in Berlin.
A man is being hunted by German police after a lorry ploughed into a Berlin Christmas market on Monday, killing 12, but who is the suspect?