A senior French police officer and his female companion were killed following an attack Monday evening by a knife-wielding man in a distant suburb of Paris, officials said.
The attacker was also killed in the ensuing confrontation with police, while a three-year-old boy was rescued by officers.
The Islamic State's Amaq news agency cited an unnamed "source" as saying an IS fighter carried out the attack, but the extremist jihadist group has not officially claimed responsibility for the attack.
The police commander was stabbed to death outside his home in Magnanville, about 35 miles (55 kilometers) west of Paris, interior minister spokesman Pierre-Henry Brandet told reporters at the scene.
The attacker then retreated indoors before elite police commandos stormed the residence. The woman and the attacker were found dead; a little boy was found safe and sound.
"The toll is a heavy one," Brandet told reporters, his voice shaking with emotion. "This commander, this police officer was killed by the individual ... (and) we discovered the body of a woman. The assailant, the criminal was killed. Thankfully, a little boy was saved. He was in the house. He's safe and sound. He was saved by police officers."
French prosecutor Vincent Lesclous -- who said he knew the slain police commander -- told reporters that the boy was found "shocked but unharmed."
"The investigation is beginning. We have no indication -- serious (indication) -- on the motivation behind this act," he said, adding that the assailant's identity was unknown
If the crime was in fact organized or inspired by IS, it would fit in with a long-established pattern of jihadist violence. France, like other countries in Europe, has seen a series of stabbings aimed at police officers or soldiers.
Although officials said the attacker was killed by police when they stormed the residence, it was unclear how the woman was killed, or what the couple's precise relation was to the rescued child.
French President Francois Hollande condemned what he described as an "odious act," saying that a meeting would be held at his Elysee office on Tuesday.
"Light will be shed on the circumstances of this abominable drama whose investigation, under the authority of justice, will determine the exact nature," Hollande said in a statement.