A series of car crashes on a Berlin highway was an extremist attack, German prosecutors have said.

According to the current state of its investigation, it was an Islamist-motivated attack, the regional office told DPA news agency.

Six people were injured, three severely, when the suspect, a 30-year-old Iraqi man, allegedly deliberately drove into several vehicles on Tuesday evening along a stretch of road in the German capital.

The incident led to the closure of one of Berlin’s main traffic arteries.

There were indications the man had mental health problems, DPA reported.

Local media said the suspect later stopped on the highway and put a box on the roof of his car, claiming it contained explosives. Specialists opened the box and found only tools. The man was detained by police.

Several media outlets also reported the man shouted “Allahu akbar” (God is great) as he got out of his car.

The incident led to long traffic jams on Tuesday evening. About 300 people were stuck on the highway for hours and receiving support from the German Red Cross, the Berlin fire department tweeted.