Islamic State posted a video on Tuesday in which a man whom it identifies as the Afghan refugee who attacked passengers with an axe on a train in Germany vows to carry out a suicide mission and urges other Muslims to do the same.In the two minute and 20 second video, entitled "Germany - Video of the Islamic State Soldier Muhammad Riyad Who Carried out the Wuerzburg Attack", a young man wields a small knife, which he says he will use to slaughter infidels and avenge the deaths of men, women and children in Muslim countries.It was not immediately possible to verify that the man in the video was the train attacker. The video was posted by Islamic State's news agency, Amaq. Islamic State claimed responsibility earlier in the day for the attack by the axe-wielding Afghan refugee, according to its online Amaq news agency."The perpetrator of the stabbing attack in Germany was one of the fighters of the Islamic State and carried out the operation in answer to the calls to target the countries of the coalition fighting the Islamic State," the statement said.Speaking on German public television, Interior Minister Joachim Herrmann said it was too early to speculate about the motives of the attacker, who had wielded an axe and a knife, and whether he was a member of an Islamist group or had become self-radicalized in recent times.The interior minister for the state of Bavaria later revealed that local authorities had discovered hand-drawn Islamic State flag in the room of the 17-year-old Afghan refugee who attacked passengers on a train in southern Germany before being shot dead by police.Herrmann said two of those injured in the attacks were in a critical condition. Several of the injured included members of a Chinese family, he said, without giving any further details. Four people were severely wounded in the attack before he was shot dead by police, the interior minister for the state of Bavaria said.