The Islamic State group claimed responsibility Tuesday for its first attack in Germany, an axe and knife assault on a train carried out by a 17-year-old Afghan refugee.

German authorities said they had found a hand-painted IS flag among the belongings of the asylum seeker, who seriously injured four members of a family of tourists from Hong Kong in his rampage. The teenage assailant was killed as he tried to flee.

"The perpetrator of the stabbing attack in Germany was one of the fighters of the Islamic State," the IS-linked Amaq news agency said.

The assault on a regional train near the southern city of Wuerzburg late Monday left two of the victims critically hurt, said Joachim Herrmann, the interior minister of Bavaria state.

"We hope that those who were gravely injured make it," Herrmann told ZDF public television.

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Germany has thus far escaped the kind of large-scale jihadist attack seen in the southern French city of Nice last week, in which 31-year-old Mohamed Lahouaiej Bouhlel used a truck to mow down 84 people. That attack was also claimed by IS.

The terrifying assault in Bavaria is likely to revive a heated national debate about integrating migrants and refugees after a record influx last year.

'Like a slaughterhouse'

The assailant had arrived as an unaccompanied minor in Germany about two years ago and had been staying with a foster family in the region for the last two weeks, Herrmann said.

"It is quite probable that this was an Islamist attack," said a ministry spokesman hours after the attack, adding that the assailant was heard shouting "Allahu akbar" (God is greatest).

However, he stressed that the investigation was ongoing and that the teenager appeared to have acted alone.

"We must determine what the motive was and to what extent he really belonged to the Islamist scene or self-radicalised very recently," Herrmann said, adding that the assailant had no criminal record in Germany.

The assault happened around 9:15 pm (1915 GMT) on the train which runs between the town of Treuchtlingen and Wuerzburg in Bavaria.

An eyewitness who lives next to the railway station told DPA news agency that the train, which had been carrying around 25 people, looked "like a slaughterhouse" with blood covering the floor.

The man, who declined to give his name, said he saw people crawl from the carriage and ask for a first-aid kit as other victims lay on the floor inside.

"The perpetrator was able to leave the train, police left in pursuit and as part of this pursuit, they shot the attacker and killed him," a police spokesman said.

Herrmann later said the teenager was shot when he attacked police while trying to escape the scene.

Political tensions

Germany has been spared major Islamist attacks but in May, a mentally unstable 27-year-old man wielding a knife killed one person and injured three others on another Bavarian regional train.

Early reports had suggested he had yelled "Allahu akbar" but police later said there was no evidence pointing to a religious motive. He is being held in a psychiatric hospital.

In February, a 15-year-old girl of Turkish origin stabbed a policeman in the neck with a kitchen knife at Hanover train station in what prosecutors later said was an IS-inspired attack.

And police in April arrested two 16-year-olds over an explosion that wounded three people at a Sikh temple, in what was believed to be an Islamist-motivated attack against an Indian wedding party at a temple in the western city of Essen.

Germany let in nearly 1.1 million asylum seekers last year, with Syrians the largest group followed by Afghans.

However the number of refugees arriving in Germany has fallen sharply as a result of the closure of the Balkans migration route and an EU deal with Turkey to stem the flow.

Bavaria is governed by the Christian Social Union (CSU), sister party to Chancellor Angela Merkel's conservative Christian Democrats, which has been loudly critical of Merkel's welcoming stance toward asylum seekers.

The split threatened the unity of the ruling coalition in Berlin and sent the government's approval ratings plunging.

It has also put wind in the sails of a right-wing populist party, Alternative for Germany, which was founded as a eurosceptic protest outfit in 2013 but now mainly rails against Islam and Germany's refugee influx.

Merkel's popularity has rebounded recently but the Bavaria attack is likely to stoke political tensions.