A man has caused a series of motorway accidents in Berlin, injuring six people including three seriously in what German prosecutors Wednesday described as a suspected Islamist attack.

Berlin police said the man caused three accidents on the Autobahn 100 in the city's Tempelhof-Schoeneberg district shortly before 7:00 pm (1700 GMT) on Tuesday evening, before claiming that a box in his car contained a "dangerous object".

Local media reported that the suspect was a 30-year-old Iraqi who had shouted "Allahu Akbar" (God is Greatest) when coming out of his mangled black Opel Astra.

"The possibility of an Islamist attack cannot be ruled out," prosecutors said in a statement.

The driver had "targeted motorcyclists in particular", they said.

"Statements by the accused suggest a religious Islamist motivation" for his actions. "There are also indications of psychological instability", they added.

The suspect has been arrested and will be brought before a judge for attempted murder.

German media reported that a motorcyclist was among the injured.

Religious slogans 

The suspect had published clues on social media that he was planning an attack, according to the DPA news agency. 

He had posted photos of the car used for the attack on Facebook, along with religious slogans, the report said, citing a spokesman for the prosecution.

"Nobody come any closer or you will all die," the Bild newspaper quoted the suspect as saying after he got out of his car and placed the metal box on the roof.

His vehicle was apparently brought to a halt after crashing into a motorbike.

However, when police opened the box using high-pressure water jets it was found to contain nothing but tools.

The motorway was closed for several hours, causing significant travel disruption, and drivers caught in traffic jams were asked to leave their vehicles as a precaution.

Investigators have not found any links to a terrorist organisation so far, prosecutors said. 

Violent attacks 

People with ties to Islamic extremism have committed several violent attacks in Germany in recent years. 

The deadliest was a truck rampage at a Berlin Christmas market in December 2016 that killed 12 people. 

The Tunisian attacker, a failed asylum seeker, was a supporter of the Islamic State jihadist group.

More recently, an Islamist and his wife were convicted of planning a biological bomb attack in Germany in 2018 with the deadly poison ricin.

The pair had ordered castor seeds, explosives and metal ball bearings on the internet to build the toxic bomb.

The man was sentenced in March to 10 years in prison while his wife received an eight-year sentence in June.

Since 2013, the number of Islamists considered dangerous in Germany has increased fivefold to 680, according to security services.

The far right has often accused Chancellor Angela Merkel of having contributed to the Islamist threat by opening the country's borders to hundreds of thousands of migrants in 2015.