Tunisia's Interior Ministry says police have arrested Anis Amri's nephew and two others suspected of belonging to the same extremist network.
The ministry says in a statement that Amri — suspected of driving a truck into a Christmas market crowd in Berlin, killing 12 — had sent his 18-year-old nephew Fedi money to join him in Europe.
It is unclear whether any of the suspects helped Amri flee Berlin.
¦Berlin attack suspect Anis Amri killed in Milan
The nephew was arrested in Amri's hometown of Oueslatia while the others were arrested in Tunis. The arrests occurred Saturday.
Officials in Spain are also looking into potential ties Amri had in that country.
Interior Minister Juan Ignacio Zoido told Spanish radio station Cope that Spanish police are looking into a tip passed on by German authorities that Anis Amri had developed a contact in Spain.
Zoido says "we are studying all possible connections (between Amri) and our country, above all with one specific person."
On Monday, Amri's fingerprints and wallet were found in a truck that plowed into the Christmas market in Berlin, killing 12 people and injuring 56 others.
After fleeing from Germany and through France, he was shot dead by Italian police in Milan on Friday.