German police on Wednesday detained a Tunisian national on suspicion of having ties to Anis Amri, the suspected Berlin truck attacker gunned down by Italian police last week, prosecutors said.

"The deceased suspect Anis Amri had saved the number of this 40-year-old Tunisian national in his phone. The investigations indicate that he could have been involved in the attack," the federal prosecutor's office said in a statement.

The suspect was taken into custody early Wednesday after federal police officers searched his home and work premises.

"The extent to which the suspicions against the detained person can be confirmed remains subject to further investigation," the statement added.

Twelve people were killed and dozens injured on December 19, when Amri is believed to have hijacked a truck and used it to mow down people at a Berlin Christmas market.

The 24-year-old went on the run and was the focus of a frantic four-day manhunt before being shot dead by police in Milan after opening fire first.

The Berlin rampage was claimed by the Islamic State group, which released a video last Friday in which Amri is shown pledging allegiance to IS chief Abu Bakr al-Baghdadi.

Tunisian authorities on Saturday announced that they had arrested Amri's nephew and two other men suspected of being members of a "terrorist cell" connected to Amri.

They made no direct link between the trio and the Christmas market attack however.