The prosecutor's office, which handles terror cases in Germany, announced Monday it had taken charge of the investigation given its "special significance."

The attacker, identified as a 26-year-old Palestinian man born in the United Arab Emirates and named only as Ahmad A., fatally stabbed one person and injured six others at a Hamburg supermarket on Friday before he was detained by passersby.

Prosecutors said in a statement that while he was a known Islamist, there was no indication he was a member of an extremist militant group like "Islamic State."

"According to ongoing investigations, the accused had self-radicalized," the statement said.

Asylum application had been rejected

The suspect, a rejected asylum seeker who came to Germany in 2015, reportedly told investigators that he had developed an interest in extremist ideology before ultimately deciding "to adopt a corresponding lifestyle" two days before the stabbing.

"On the day of the act, he resolved to commit an attack with the hope that he would die as a martyr," prosecutors added.

The suspect is alleged to have entered a supermarket in Hamburg's Barmbek district before taking a kitchen knife from a shelf and embarking on a stabbing spree. He killed a 50-year-old man and injured several other people.

Witnesses told news agency Agence France Presse he shouted "Allahu Akbar" ("God is the Greatest") as he fled the scene, but that bystanders chased after him and managed to stop him.

He is currently in police custody on suspicion of murder and five counts of attempted murder.

Officials acknowledge that Ahmad A. was known to them as an Islamist, but they say he had never been classified as a "threat." Plans to deport him had been put on hold because he didn't yet have valid papers. 

Germany has been on high alert, with boosted security in many cities, particularly since last December when 12 people were killed in a truck attack at a Berlin Christmas market.   

nm/se (AFP, AP, dpa)