"My personal view is that I unfortunately think it's very likely this really was an Islamist suicide attack," Bavarian interior minister Joachim Herrmann told German news agency dpa.
The 27-year-old Syrian blew himself up after being turned away from an open-air music festival. Herrmann said the man's request for asylum was rejected a year ago, but he was allowed to remain in Germany because of the strife in Syria.
"The obvious intention to kill more people indicates an Islamist connection," he told dpa.
Earlier today, a spokesman for the prosecutor's office in Ansbach said the attacker's motive wasn't clear.
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"If there is an Islamist link or not is purely speculation at this point," said the spokesman, Michael Schrotberger.
Roman Fertinger, the deputy police chief in nearby Nuernberg, said it was likely there would have been more casualties if the man had managed to enter the concert venue.
The explosion came as Germany, and the southern state of Bavaria in particular, have been on edge.
Earlier yesterday, a Syrian man killed a woman with a machete and wounded two others outside a bus station in the southwestern city of Reutlingen before being arrested. Police said there were no indications pointing to terrorism.
Two days earlier, a man went on a deadly rampage at a Munich mall, killing nine people and leaving dozens wounded. And an ax attack on a train near Wuerzburg last Monday wounded five. A 17-year-old Afghan asylum-seeker was shot and killed by police as he fled the scene.
The three-day open-air concert was underway, with about 2,500 in attendance, when it was shut down as a precaution after the explosion. Jethro Tull frontman Ian Anderson was the scheduled performer.
Bavarian public broadcaster Bayerische Rundfunk reported that 200 police officers and 350 rescue personnel were brought in following the explosion in Ansbach.