Extremist motive 'likely' in deadly German knife attack

German investigators said Tuesday they suspected an extremist motive behind a deadly knife attack by a Somali man, risking reopening a divisive migration debate during the country's general election campaign.

Authorities in the state of Bavaria said evidence was mounting that the suspect, a Somali asylum seeker with a history of mental problems and only temporary permission to remain in Germany, may have been radicalised.

The Bavarian Central Office for Extremism and Terrorism believes the man's actions were due to extremist violent stands of Islamist ideology.

The 24-year-old man on Friday went on a knife rampage in the city of Wuerzburg, stabbing three women to death and leaving six other people seriously injured.

The Somali suspect, who arrived in Germany in 2015, struck in the city centre, first at a household goods store before moving on to a bank.

He was cornered by bystanders, then overpowered by police after they shot him in the thigh.

Investigators found records showing that the man had been treated at a psychiatric institution, and police said he was not a known extremist.

However the Bavarian authorities said a number of factors made an extremist motive appear probable.

These included witness accounts that suspect cried "Allahu Akbar" ("God is greatest" in Arabic) during his killing spree and spoke of "jihad" from his hospital bed after he was taken into custody.

- 'Directed at all humanity' -

The German government has been hesitant to classify the assault as a terror attack and urged the public to wait until the investigation is complete before drawing conclusions.

Chancellor Angela Merkel said "what is certain is that the horrific act is directed at all humanity and every religion", her spokesman Steffen Seibert tweeted on Saturday.

However the mass-selling Bild newspaper accused the government of turning a blind eye to indications of a radical motive, while the conservative broadsheet Frankfurt Allgemeine Zeitung said Germany needed to "bid farewell to its illusions" about migration.

Meanwhile the far-right AfD party in particular has seized on the violence ahead of the September 26 general election.

The anti-immigration, anti-Islam party's co-leader Joerg Meuthen called the attack a "tragedy for the victims, who have my sympathy" as well as "another manifestation of Merkel's failed migration policy".

The AfD has railed against Merkel's decision to allow in more than one million asylum-seekers -- many fleeing Iraq and Syria -- since 2015, arguing it has contributed to a heightened security risk.

However the party has slipped in the polls as the pandemic supplanted immigration as a subject of concern for most German voters.

The three main candidates to replace Merkel as chancellor have remained notably circumspect, with the assault barely garnering a mention at a televised debate on Saturday.

They instead noted the "civic courage" of bystanders who confronted the suspect, possibly preventing further violence.

Mainstream politicians and news outlets highlighted one man in particular, a Kurdish asylum seeker from Iran, who in a mobile phone video that went viral could be seen cornering the knife-wielding man by swinging a backpack at him.

Bavarian state premier Markus Soeder promptly promised the man a medal, while a debate began online on whether the man, Chia Rabiei, could be given German citizenship as a reward for his heroism -- a step migration authorities said was unlikely.