A Tunisian man has been arrested on suspicion of being involved in last week's truck attack on a Christmas market in Berlin.
German federal prosecutors said the 40-year-old was detained during a search of his home and business.
Officials said the man's number was saved in the mobile phone of Anis Amri, a fellow Tunisian believed to have driven a truck into the market on December 19.
They said further investigations indicate that the arrested man "may have been involved in the attack".
Twelve people died in the attack in the German capital.
Prosecutors have until Thursday evening to determine whether the case against the man holds up to the extent they can seek a formal arrest warrant.
This would allow them to keep him in custody pending possible charges.