BERLIN — The Islamic State claimed responsibility today for an ax-and-knife attack on a German train that left at least five people injured, but authorities said the 17-year-old Afghan asylum seeker who was shot and killed by police as he fled the scene appears to have self-radicalized and had no direct link to the extremist group.

The teenager shouted “Allahu akbar” (“God is great”) as he attacked people on the regional train near the Bavarian city of Wuerzburg on Monday night, and a hand-painted flag of the Islamic State was found during a search of his room, according to state Interior Minister Joachim Herrmann.

Though the Islamic State group claimed responsibility through its Aamaq news agency, Herrmann said the suspect, whose identity has not been released, had written notes in his native Pashto that indicated he may have been self-radicalized and there was “no indication” he was directly connected to the IS group.

Herrmann said people close to the attacker told investigators he had seemed like a calm person, not overtly religious or an extremist.

Herrmann said investigators were still looking into the evidence found in the teenager’s room, saying it could be possible that the notes included a farewell letter to his father.

The 17-year-old attacked at least four passengers with an ax and knife on the train near Wuerzburg-Heidingsfeld, but was shot and killed by a special police unit which happened to be nearby.

Four people on the train were injured, along with a woman outside as the attacker fled.

Herrmann said that it was too early to draw conclusions about the attacker’s motive.

German officials did not identify the victims, but Hong Kong’s immigration department said that among those injured in the attack were four members of a family of five from the southern Chinese city.

The university hospital in Wuerzburg confirmed that it was treating three patients with life-threatening injuries, including two from Hong Kong.

Hong Kong’s top official, Chief Executive Leung Chun-Ying, condemned the attack and extended his sympathies to the victims and their families.

The dpa news agency reported that the attacker injured the 62-year-old father, the 58-year-old mother, their adult daughter and her boyfriend. The teenage son was not injured. The father and the boyfriend had tried to defend the other family members, dpa said.

The assailant jumped off the train after someone pulled the emergency cord and got about 500 yards into Wuerzburg-Heidingsfeld, attacked a woman there with his ax and ran away before the police special unit chased him.

As police drew near, the assailant started attacking the officers and was shot, according to Herrmann.