HAMBURG: The suspect who killed a man with a knife in Hamburg supermarket was a known Islamist, German officials said Saturday, adding that his motives remained unclear as he also suffered from psychological problems, reports AFP.

Identified as a 26-year-old man of Palestinian origin, he had arrived in Germany in 2015, but was due to be deported as his application for asylum was rejected.

The assault risks reopening a bitter debate over refugees two months before general elections, putting pressure on Chancellor Angela Merkel over her decision to open Germany's borders in 2015, letting more than a million asylum seekers in.

"He was known as an Islamist but not a jihadist," said the German port city's interior minister Andy Grote, noting "there are indications of radicalisation".

But the minister stressed that while there could have been an Islamist motive for the attack, the suspect also suffered from "psychological instability".

"It remains unclear which was the overriding element," he said.