The Syrian bomber, who blew himself up in southern Germany, wounding 15 people, had pledged allegiance to Islamic State. It is confirmed by the video found on his mobile phone, the Bavarian Interior Minister said on Monday.
The bomber, who has been named as Mohammad Daleel, also threatened to attack Germany on mobile phone footage discovered by police.
Nuremberg police found the same materials used in the bomb during the search - diesel, hydrochloric acid, alcohol, batteries, paint thinner and pebbles. They also discoverd computer images and film clips linked to the militant group, police said.
"A provisional translation by an interpreter shows that he expressly announces, in the name of Allah, and testifying his allegiance to (Islamic State leader) Abu Bakr al-Baghdadi ... an act of revenge against the Germans because they're getting in the way of Islam," Bavarian Interior Minister Joachim Herrmann told a news conference.
"I think that after this video there's no doubt that the attack was a terrorist attack with an Islamist background."
The ISIS-linked Amaq Agency has claims the suicide bombing was carried out by "soldier of Islamic State".
Nuremberg police chief Roman Fertinger said the influence of Islamic State could be seen on the bomber's computer.
"There was also a laptop that showed pictures and film sequences that glorify violence and are unequivocally linked to Islamic State," he told a news conference.Read also: "12 wounded over terrorist attack in Ansbach, Germany"
The attack on festival in Ansbach was the fourth act of violence by men of Middle Eastern or Asian origin against German civilians in a week.
The 27-year-old bomber arrived in Germany two years ago and claimed asylum, a federal interior ministry spokesman said. He was faced deportation to Bulgaria, because of troubles with police.