The Syrian man who blew himself up and injured 15 other people outside a crowded music festival was facing deportation to Bulgaria, a German interior ministry spokesman has said.

The 27-year-old failed asylum seeker detonated an explosive device near a bar in central Ansbach on Sunday evening after being refused entry to the festival because he did not have a ticket.

The attacker's rucksack contained sharp pieces of metal. Four of those injured are in a serious condition.

Explosion in Ansbach, Germany

"Syrians cannot at the moment be deported to Syria at the moment, but that doesn't mean that Syrians overall cannot be deported," Tobias Plate told a regular government news conference.

"The Syrian in Ansbach was facing deportation and this was to Bulgaria," he added.

Mr Plate said the man had received two deportation notices, most recently being told on 13 July that he would be deported to Bulgaria

He says the man was to be deported to Bulgaria because he had submitted his first asylum request in the southeastern European country.

A government spokeswoman told the same news conference that it was too early to decide on changes to Germany's refugee policy before the results of the investigation into the attack were published.

"The acts of the last days and weeks do not show a uniform picture," Ulrike Demmer said. "Most terrorists who carried out attacks in Europe over the last months were not refugees."

A team of 30 investigators are examining evidence related to the bombing (EPA)

The man had been living in Germany for two years and had received psychiatric treatment, including twice for attempted suicide, authorities said.

Last year his application or asylum was rejected by German authorities, though due to the Syrian civil war he had been allowed to stay in the country.

On Monday, armed police were seen at two addresses the man had lived at looking for evidence. Police said the attacker had also been known for drug possesion.

An Islamist link could not be ruled out, Bavarian Interior Minister Joachim Herrmann told reporters earlier - saying in his view “it's very likely this really was an Islamist suicide attack” with a clear intention to cause multiple casualties.

“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,” Mr Herrmann said.

He said investigators had yet to determine the motive of the attacks. “Because the rucksack and this bomb were packed with so many metal parts that could have killed and injured many more people, it cannot simply be considered a pure suicide attempt," he added.

Mr Herrmann told Reuters the recent attacks raised serious questions about Germany's asylum law and security nationwide. He planned to introduce measures at a meeting of Bavaria's conservative government on Tuesday to strengthen police forces, in part by ensuring they have adequate equipment.

The explosion is the fourth attack to hit Germany in a week, following Friday's massacre in Munich that left nine dead and dozens injured and an Isis-inspired axe rampage by a teenager last Monday.

Earlier on Sunday, a 21-year-old Syrian refugee was arrested after killing a pregnant woman and wounding two people with a machete in the southwestern city of Reutlingen, near Stuttgart.

Ansbach resident Thomas Debinski said people panicked when they heard the explosion, especially after the events of the past week, and it soon became clear that someone had set off a bomb in a rucksack.

“After what just happened in Munich, and today in Reutlingen, what you hear about, it is very disturbing, when you know that such a thing can happen so close to you, in such a small town as Ansbach,” Mr Debinski said.