WUERZBURG, Germany » A 17-year-old Afghan asylum-seeker vowing “revenge on these infidels” went on an ax-and-knife rampage on a train in southern Germany, wounding five people before being shot and killed by police — an attack that German authorities conceded today was almost impossible to prevent.

German officials didn’t identify the attacker or the victims, but Hong Kong’s immigration department said among those wounded were four members of a family of five from the southern Chinese city.

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

At least one member of the Chinese family and another woman attacked outside the train were in life-threatening condition, according to Bamberg prosecutor Erik Ohlenschlager.

The Islamic State group claimed responsibility for the Monday night train attack, which came less than a week after the Bastille Day truck attack in Nice, France, also claimed by IS, in which 84 people were killed.

Bavaria’s top security official Joachim Herrmann said, while the Nice attack was “clearly another dimension,” in both cases the choices of weapons and targets made them “extremely difficult to prevent in any fashion.”

“In one case a truck, in another an ax and knife — those are the weapons that society cannot logically eliminate, with which any person could equip themselves, which they could put to use at virtually any location at any time of night or day,” he said.

Nevertheless, he urged an increased visible police presence across the country.

Germany has not experienced the large, deadly attacks that France and Belgium have, although a string of sexual assaults and robberies on New Year’s Eve in Cologne that prosecutors say were committed largely by foreigners gave rise to fears of whether the country could cope with the 1 million migrants it registered in 2015.

As the flow of migrants has slowed this year, the anti-immigrant protests have faded, but the train attack seemed likely to raise concerns again.

In a video posted by the Islamic State that purports to show the attacker — but could not be immediately verified as authentic — the young man calls on others to “kill these infidels in the countries that you live in.”

“You can see I have lived in your own home and have planned to behead you in your own territory,” the young man says in Pashto while brandishing a knife.

Despite the IS claim of responsibility and a hand-painted IS flag found in the suspect’s apartment, authorities said so far they have found no direct links between the suspect and IS and believe that he self-radicalized.

Investigator Lothar Koehler said the teenager’s motivation appeared to be Islamic extremism based upon a passage, found among notes in his apartment, which read: “Pray for me that I can take revenge on these infidels and pray for me that I will go to heaven.”

In the premeditated attack, the attacker boarded the regional train after 9 p.m. near the Bavarian city of Wuerzburg with an ax and knife concealed in a bag, according to Ohlenschlager. He said the suspect had learned Saturday that a friend had died in Afghanistan.

On the train, the suspect encountered an employee from the asylum shelter where he had lived until two weeks ago when he moved in with a foster family. He didn’t respond to her comments but left for another train car, hid in a bathroom and armed himself, Ohlenschlager said.

“Then, without warning, he attacked the passengers using great force on their bodies and their heads,” Ohlenschlager said, adding he shouted “Allahu akbar,” Arabic for “God is great.”

Witnesses said the interior of the train was covered with blood and looked “like a slaughterhouse,” the German news agency dpa reported. About 30 passengers were on the train and more than a dozen were treated for shock.

After the train made an emergency stop, the suspect fled and ran into two women walking a dog. He attacked one from behind, saying “I’ll finish you!” and yelling a vulgar term for a woman in German, as he hit her at least twice in the face with the ax.

Shortly after, he encountered a police SWAT team, jumping out at them from bushes brandishing his ax. He was shot and killed.

Ohlenschlager said at least two victims were suffering from “acute life-threatening” wounds, including the woman attacked outside the train.

In the video posted by the Islamic State’s Aamaq news agency, the man claimed he was a soldier “of the Islamic State and will be carrying out an attack in Germany today.”

Chancellor Angela Merkel’s chief of staff, Peter Altmaier, said on ZDF television the video was still being evaluated but that Germany’s security agencies believe it to be authentic.

Herrmann said people close to the attacker told investigators he had seemed to be a calm person, not overtly religious or an extremist. He said investigators were still looking into the evidence found in the teenager’s room, including a possible farewell letter to his father.

Koehler said the suspect had registered as a refugee in June 2015, when he crossed into the country from Austria. German authorities sent him to an asylum home for unaccompanied minors in Ochsenfurt. He received asylum in March and had a residency permit.

He was a Sunni Muslim who didn’t go to the mosque regularly, but prayed regularly at home, and had not committed any previous crimes in Germany Koehler said.

“He was active on social media, had his page there, but there were no hints of any extremist Islamist thought,” Koehler said. “However, 24 hours ago he posted a cryptic message about the enemies of Islam.”

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