Prosecutors in the northern German city of Flensburg said on Tuesday that a youth arrested last week was planning an Islamist terror attack.

He had "sufficiently concrete plans for an attack" to warrant an arrest, they added, saying there was also evidence of his radicalization.

The young man had been detained a week earlier in the town of Elmshorn and remains in custody while police continue the investigation.

Authorities have not confirmed much about the suspect, including how they caught wind of his plan or the details of his arrest.

What was he planning?

However, they have said that he planned to utilize a large vehicle, such as a truck, for an attack.

This is reminiscent of a December 2016 assault on a Christmas market in Berlin, when Anis Amri deliberately drove into pedestrians, killing 13 people and injuring 70.

Amri fled to Italy and was killed in a shootout with police several days later.

es/wmr (AFP, dpa)