Emergency workers and vehicles are seen following an explosion in Ansbach, near Nuremberg July 25, 2016, in this still image taken from video. [Photo/Agencies]

BERLIN - An explosion killed at least one person and injured 12 others near the German city of Nuremberg on Sunday and authorities said it was believed to be intentional.

A police spokesman said the person killed in the blast, a man with a backpack, was likely carrying an explosive device and acted alone.

There was no immediate information on his identity but the spokesman added that three of the 12 people injured were in serious condition.

It was the fourth violent incident in Germany in a week and came as the country was still on edge after the killing of nine people by an 18-year-old Iranian-German gunman in Munich on Friday.

The blast outside a restaurant in the town Ansbach prompted the evacuation of more than 2,000 people from a nearby "Ansbach Open" music festival, police said.

"We assume it was a deliberate explosion," a Bavarian Interior Ministry spokesman said.

He said no arrests had been made in connection with the explosion but Bavarian Interior Minister Joachim Herrmann was en route to the site.

The mayor of Ansbach told reporters the blast was caused by an explosive device, according to the Nordbayern.de news website.

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

That attack came after a refugee from Pakistan wielding an axe injured five people near Wuerzbuerg, also in southern Germany, before he was shot dead by police on July 18.

Ansbach is home to a US Army base and the 12th Combat Aviation Brigade. A spokesman at the base said the base had no information about the explosion.

There was no immediate word on possible motives for the explosion, but police said neither Sunday's machete attack nor Friday's shooting in Munich bore any sign of connections with Islamic State or other militant groups.

Islamic State claimed responsibility for the July 18 axe attack in Germany. It also claimed responsibility for the July 14 attack in which a Tunisian man drove a truck into Bastille Day holiday crowds in the French city of Nice, killing 84 people.