German police have arrested a man who is “to the highest degree” suspected of fatally stabbing three people at a festival in the city of Solingen on Friday, an official of North-Rhine Westphalia state said.

Herbert Reul, the state’s interior minister, declined to elaborate on details in an interview with public broadcaster ARD, saying the investigation was ongoing. He said police found evidence related to the arrested person, the target of a manhunt.

The Islamic State claimed responsibility for the attack “to avenge Muslims in Palestine and everywhere,” the Associated Press reported earlier Saturday, citing a news site tied to the terror group.

A “soldier of the Islamic State” carried out an attack against Christians, according to the Amaq news site, AP said. Reul declined to say whether German authorities believed the IS statement was authentic.

Eight people were injured in the incident, which is likely to stoke further controversy around immigration laws, a controversial issue in Germany and other European countries with active populist parties on both the extreme right and left. Polls show that the German anti-immigration parties AfD and BSW may surge in elections in the Thuringia and Saxony regions next weekend.

The city of Solingen, which was celebrating 650 years since its founding, canceled the festival after the attack.