A man who blew himself up at a bar in the southern German town of Ansbach on Sunday was in an online chat with an as-yet unknown person immediately before the explosion, Bavaria's interior minister said on Wednesday.

"There was apparently an immediate contact with someone who had a significant influence on this attack," Joachim Herrmann said, according to news agency dpa.

Herrmann said it wasn't clear whether the assailant was in contact with ISIS or where the other person in the chat was.

Investigators checking the assailant's cellphone came across the "intensive chat" and that "the chat appears to end immediately before the attack," Herrmann said.

The interior minister also said it's unclear if the bomber, Mohammad Daleel, meant to detonate his device when he did.

"Because of witness testimony on what happened and also the course of the chat, there are indeed questions about whether he intended to set off the bomb at that moment," Herrmann said.

Daleel, a Syrian asylum-seeker, died and 15 people were wounded when the bomb exploded in a wine bar Sunday night after he wasn't allowed entry to a nearby open-air concert because he didn't have a ticket.