TRAPPES, France (AP) — A man flagged by French authorities as a suspected radical killed his mother and sister and seriously injured another woman in a knife attack Thursday that was quickly claimed by the Islamic State group.

Police shot and killed the man. His motives weren’t immediately clear. Authorities didn’t rule out a family dispute and prosecutors were not immediately treating the attack as a terrorism case.

Three French officials identified the two people killed in the attack in Trappes and the mother and sister of the attacker.

The officials spoke on condition of anonymity because they weren’t authorized to give such details publicly. The third victim, a passerby who was gravely injured in the attack, was also a woman, one of the officials said.

The Islamic State group, via its Aamaq news agency, claimed responsibility. The agency said the attack in Trappes was motivated by calls from the IS leadership to attack civilians in countries at war with the extremist group. Hours earlier, IS leader Abu Bakr al-Baghdadi urged followers to attack enemies everywhere by all means, including in knife attacks.

Police officials said the man was flagged in a government database of suspected religious and political extremists. They spoke on condition of anonymity because they weren’t authorized to discuss the investigation publicly.

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By JOHN LEICESTER and ELAINE GANLEY , Associated Press

Leicester and Lori Hinnant contributed from Paris.