Authorities continue to search for perpetrator of knife attack that killed three people in western Germany.

ISIL (ISIS) has claimed responsibility for a knife attack in Solingen, Germany that killed three people and wounded eight others, according to the group’s Amaq news site.

In a statement on Saturday, the group said the perpetrator targeted Christians and was a “soldier of the Islamic State” who carried out the attack “to avenge Muslims in Palestine and everywhere”.

The attack took place on Friday evening as thousands gathered at a central square for celebrations to mark Solingen’s 650th anniversary on Friday. The slain victims included one woman and two men.

Markus Caspers, from the counterterrorism section of the public prosecutor’s office, told a news conference on Saturday that authorities have not found the perpetrator.

“So far, we have not been able to identify a motive, but looking at the overall circumstances, we cannot rule out” the possibility of terrorism, Caspers said, though he did not offer further details.

A 15-year-old boy was arrested early on Saturday. Caspers said he was arrested after two female witnesses contacted police. They said they had listened to a conversation between the boy and an unknown person before the attack, speaking about intentions that corresponded to the events that followed.

Police, including special forces, also raided a home for asylum seekers in Solingen’s city centre, the German news agency DPA reported.

“We have received tips and therefore, we are currently conducting police activities,” a police spokesperson said.

Thorsten Fleiss from the German police, the chief of operations on Friday night, said it was a “big challenge” to bring together available evidence and testimony from witnesses to come up with an overall picture.

Meanwhile, police have warned people to stay vigilant until the perpetrator is found.

Germany’s Minister of the Interior and Community Nancy Faeser paid a visit to Solingen on Saturday evening. She said the government would do everything possible to support the city and its people.

“We will not allow that such an awful attack divides our society,” she said, appearing alongside Minister-President of the State of North Rhine Westphalia Hendrik Wust and State Minister for Internal Affairs Herbert Reul.

Wust described the attack as “an act of terror against the security and freedom of this country”. But Faeser, the country’s top security official, has not classified it as a terror attack.

At its peak, ISIL controlled large stretches of territory in Iraq and Syria and carried out several deadly attacks across the world. But the group faced a territorial defeat in 2017, and its brutal rule collapsed after it lost all of the areas it controlled to the Iraqi government and various parties in the Syrian civil war.

The group has previously claimed responsibility for attacks that it was not involved in, including a mass shooting in Las Vegas in 2017.

In Solingen, the police cordoned off the square on Saturday and passers-by placed candles and flowers outside the barriers.

Authorities also established an online portal where witnesses could upload footage and any other information relevant to the attack, while churches in Solingen opened their doors to offer a space for prayer and emergency pastoral care.

“We are full of shock and grief,” Solingen Mayor Tim-Oliver Kurzbach told journalists.

The Festival of Diversity, marking Solingen’s 650th anniversary, began on Friday and was supposed to run through Sunday, with several stages in central streets offering attractions such as live music, cabaret and acrobatics.

Authorities have now cancelled the remainder of the festival.