Two home-made explosive devices have been detonated outside a mosque and a conference centre in the eastern German city of Dresden.
No people were injured in the incident, and there is no immediate report on the extent of damage from the explosions which took place late on Monday.
Police president Horst Kretschmar said: “Even though we do not have a letter of confession, we must assume there’s a xenophobic background.”
German interior minister Thomas de Maiziere called the attacks “outrageous”.
He said: "Aggression against people who are practising Islam is increasing in Germany.
“Fortunately, people didn’t get hurt, but we don’t want these things to happen in Germany.”
Police said they found pieces of the devices in front of the buildings.
An imam with his wife and two sons were inside the mosque at the time. They were not injured, but the entrance door was forced into the building by the blast.
Police have increased security outside mosques all over Dresden.
“I looked out of the window and saw how somebody with a motorcycle helmet threw something,” the imam’s son, Ibrahim Turan, told the Bild newspaper.
“First I thought it was a stone, but then there was a loud bang and the door was on fire.”
The second device exploded shortly after the first on a terrace between a hotel and the International Congress Centre, a facility which can accommodate 6,000 people.
The blast destroyed a decorative glass block on the outdoor terrace. Police evacuated the hotel bar and asked people to stay away from windows at the hotel building.
About 50 officers were involved in the overnight operation, police said.
Mr Kretschmar said the two explosions could have also been connected to Germany’s national unification celebrations next Monday, which will be held in Dresden.
Dresden is the state capital of Saxony, which has seen a number of racist attacks recently.
The German government published a report last week warning that there had been an increase of racist and far-right attacks in eastern Germany which it called “a big threat for the development of the society and economy”.
PA