A man pledging allegiance to so-called Islamic State has stabbed a French police commander to death outside his home.
He also took the officer's partner and their three-year-old son hostage in their home in Magnanville, near Paris.
The attacker - who was reportedly shouting "Allahu akbar" (God is greater) as he stabbed the officer - was shot dead by armed officers when they stormed the property.
The officer's partner was found dead but the child survived.
Islamic State's Amaq news agency said one of the group's fighters was responsible for the killing.
French prosecutors have launched an anti-terror investigation into the incident which Francois Hollande condemned as an "odious act".
The French president will chair a meeting at the presidential palace on Tuesday.
The attacker stabbed the 42-year-old police commander, who was not in uniform, multiple times outside his home before forcing his way inside and taking the woman and child hostage.
He reportedly made reference to IS during negotiations with police.
“Negotiations were opened but it became clear that they would not succeed and police then entered the home, where they found the body of a woman,” a spokesperson for the French ministry is quoted as saying.
Residents reported hearing loud explosions as armed officers launched their operation at around midnight.
The rescued child was said to be “shocked but unharmed”.
The killing comes a day after a gunman - who also pledged allegiance to Islamic State - shot dead 49 people at a gay nightclub in Orlando, in the deadliest mass shooting in US history.
France, which is currently hosting Euro 2016, has been on a state of high alert since November's terrorist attacks in Paris which left 130 people dead.