A senior German official says the new suspect in the Christmas market truck attack had been considered a possible terror threat by authorities.

"This person has been noticed by various security authorities in Germany in the context of contacts to a radical Islamic circle. I cannot go into detail on this," said Ralf Jaeger, Interior Minister of North Rhine-Westphalia. 

Suspect left Tunisia seven years ago, had spent time in Italian prison

Authorities have identified the suspect as 24-year-old Anis Amri. The federal prosecutor's office has offered a reward of up to 100,000 euros, or U.S. $140,0000, for information leading to his capture.

Tunisian media say Amri left the country seven years ago as an illegal immigrant and had served jail time in Italy.

Officials say the Tunisian appears to have arrived in Germany last July and his asylum application was rejected. He also may have used different names. German police commandos raided two apartments in Berlin late on Wednesday but did not find Amri.