The ISIS group on Tuesday released a video purportedly showing the Afghan refugee — who slashed people on a German train and was later shot dead — threatening “infidel” countries and saying he would carry out the attack.

The video released by ISIS-affiliated Amaq news agency, subtitled in Arabic, shows teenager “Mohammed Riyadh” — knife in hand — announcing in Pashto that he would carry out an “operation” in Germany, and presenting himself as a “soldier of the caliphate”. Amaq had earlier said the assailant, who seriously wounded four tourists from Hong Kong wielding an axe and a knife on Monday, was an ISIS “fighter”. In the video that lasts two minutes 20 seconds, the 17-year-old says “soldiers of the caliphate” will attack “infidels” everywhere.

On Monday, at 7.15 pm GMT, the teenager seriously injured four passengers on a local train in Bavaria.

Authorities in Germany said they found a hand-painted ISIS flag among the belongings of the asylum-seeker, who was killed by the police as he tried to flee after the attack.