German police commandos raided two apartments in Berlin's Kreuzberg neighborhood on Wednesday but did not find a Tunisian man suspected of involvement in a deadly truck attack, Die Welt newspaper reported, citing investigators.

It said investigators believed that Anis Amri may have been in one of the two apartments. Police forces had to overpower a man at one of the apartments, the paper said. It gave no further information.

Germany on Wednesday offered a reward of up to 100,000 euros ($104,260) for information leading to the arrest of a Tunisian man suspected of involvement in the Berlin truck attack, identifying him as 24-year-old Anis Amri who could be armed and dangerous.

The Federal Prosecutor's Office (GBA) said in a statement that a search for Amri was underway, with support from police forces in all of Germany's 16 federal states.

"Anis AMRI is 178 cm tall and weighs about 75 kg, has black hair and brown eyes," the office said in the statement. "Beware: He could be violent and armed!"

Two pictures of Amri were published on the GBA's website.

A Tunisian man suspected in the Berlin Christmas market attack left Tunisia seven years ago as an illegal immigrant and spent time in prison in Italy, his father and security sources told Tunisia's Radio Mosaique on Wednesday.

The radio reported on its website that security sources had named the suspect as Anis Amri from Oueslatia in rural central Tunisia. He served four years in jail in Italy on accusations of burning down a school, it said. The father told the radio station that his son had left for Germany a year ago.

A Tunisian interior ministry spokesman did not immediately return a call seeking confirmation of the radio report.

German authorities began looking for a Tunisian asylum seeker as a suspect after finding an identity document under the driver's seat of the truck that ploughed into a Berlin Christmas market in the deadliest attack on German soil since 1980. Twelve people were killed.

Mosaique said the suspect had also been accused of violent robbery in Tunisia. Amri, 24, had contact with his brothers, but not his father, it said. Authorities were questioning the father about possible links to Islamic State, the radio said, citing security sources.

Oueslatia, near the historic religious city of Kairoaun, is like many marginalised, rural Tunisian towns where unemployment is high and opportunities scarce for young men. Several families there have lost sons who joined jihadist groups in Iraq, Syria and Libya.

More than 4,000 Tunisians have left to join Islamic State and other militant groups overseas, recruited by hardline preachers or online networks. Tunisia was hit last year by three major militant attacks, two targeting foreign tourists, by gunmen who spent time in jihadist camps overseas.