The so-called Islamic State group has released a video purportedly showing the Afghan refugee who slashed people on a German train saying he would carry out the attack and threatening "infidel" countries.
The video released by IS's affiliated Amaq news agency, subtitled in Arabic, shows teenager "Mohammed Riyadh" - knife in hand - announcing in Pashto he would carry out an "operation" in Germany, and presenting himself as a "soldier of the caliphate".
Amaq had earlier said the assailant who wounded five tourists from Hong Kong wielding an axe and a knife yesterday "was one of the fighters of the Islamic State".
In the video that lasts two minutes 20 seconds, the 17-year-old says "soldiers of the caliphate" will attack "infidels" everywhere.
The attack on a train near the southern city of Wuerzberg appeared to be the first time IS has claimed an attack in Germany.
Authorities in Germany said they had found a hand-painted IS flag among the belongings of the asylum-seeker, who was killed by police as he tried to flee after the attack.
"We have several badly wounded from the attack - five altogether - of which two victims are in a life-threatening condition," a police official said.
The attacker was an Afghan refugee, who had arrived as an unaccompanied minor in Germany and was staying with a foster family in the region.
IS has claimed multiple attacks carried out in its name via Amaq or its official media outlets, regardless of whether the perpetrators have any direct links with the group.
The group has regularly urged followers to target "disbelievers", with its spokesman Abu Mohamed al-Adnani in September 2014 calling on supporters to use stones, knives or vehicles as weapons.
"It is quite probable that this was an Islamist attack," said a ministry spokesman, adding that the assailant had shouted "Allahu akbar" (God is greatest).
Meanwhile, France has said it is carrying out strikes "every day" against IS jihadists in Iraq, as the country reeled from the carnage in Nice.
"There were French strikes last night in Tal Afar, not far from Mosul," Defence Minister Jean-Yves Le Drian told France Info radio.
"We don't announce it every day but since we are in the coalition we are striking every day," he said, referring to the US-led alliance engaged in an aerial campaign against IS.
IS claimed responsibility for last week's massacre in the Riviera city of Nice, where a man driving a truck ploughed into a crowd gathered for Bastille Day fireworks, killing 84 people.
Investigators say Mohamed Lahouaiej Bouhlel, the 31-year-old Tunisian driver, had shown "recent interest" in IS propaganda but they have no evidence he had any ties to the group.
Defence ministers from countries engaged in the anti-IS coalition will meet in Washington tomorrow.
