Fifteen people were injured — four of them seriously — in the blast, which occurred just two days after a gunman killed nine people at a mall in Munich.
The 27-year-old was turned away from the event by security workers in Ansbach, a town of 40,000 people southwest of Nuremberg that is also home to a U.S. Army base. He was wearing a backpack carrying explosives and metal projectiles.
Bavarian Interior Minister Joachim Herrmann said a video was found on the bomber's phone showing him pledging allegiance to ISIS and announcing "revenge" against Germany "for standing in the way of Islam."
Officials said the bomber's request for asylum in Germany was rejected a year ago because he had already been granted leave to remain by Bulgaria. The hotel where he had been staying was raided early Monday by police looking for evidence.
Roman Fertinger, the deputy police chief in nearby Nuremberg, said more casualties were likely if the bomber had managed to enter the open-air concert venue....
Hermann said the man had been under psychiatric treatment after at least two previous suicide attempts.
"It's terrible...that someone who came into our country to seek shelter has now committed such a heinous act and injured a large number of people who are at home here, some seriously," he told a news conference.
"It's a further, horrific attack that will increase the already growing security concerns of our citizens. We must do everything possible to prevent the spread of such violence in our country by people who came here to ask for asylum."
Ansbach mayor Carda Seidel said the bomber was one of 644 refugees living in the town, and confirmed reports that he was due to be deported back to Bulgaria imminently.
Earlier Sunday, another Syrian man seeking asylum used a machete to kill a woman after an argument at the central Omnibus station in Reutlingen, about 22 miles south of Stuttgart, local police said.
The 21-year-old attacker injured another woman and a man before he was arrested a few minutes later close to the crime scene.
Reutlingen is 130 miles west of Munich, where nine people were killed by an 18-year-old gunman in a city shopping center Friday."