ST.-ÉTIENNE-DU-ROUVRAY, France — Attendance was sparse at the 9 a.m. Mass Tuesday at the Église St.-Étienne, a 17th-century church in a working-class town in Normandy. Many regular parishioners were on vacation; so was the parish priest.

Mass was ending around 9:30 a.m. when two young men with knives burst in. They forced the auxiliary priest, the Rev. Jacques Hamel, 85, to kneel. When he resisted, they slit his throat. They held several worshipers and at least one nun hostage, while another nun escaped. Officers from a specialized police unit descended on the church. A short while later, officers shot the young men dead.

The brutality in St.-Étienne-du-Rouvray, a suburb of Rouen in northern France, was the latest in a series of assaults that have left Europe stunned, fearful, and angry. President François Hollande raced to the town and blamed the Islamic State for the attack; soon after, the terrorist group claimed responsibility, calling the attackers its soldiers.

It was the fourth attack linked to the Islamic State in Western Europe in less than two weeks, after a Bastille Day rampage in Nice that killed 84 people; an ax and knife attack on a train in Wuerzburg, Germany, that injured five people; and a suicide bombing at a wine bar in Ansbach, Germany.

“We must realize that the terrorists will not give up until we stop them,’’ Hollande said after meeting with the priest’s family and the town’s mayor. “It is our will. The French must know that they are threatened, that we are not the only country — Germany is, as well as others — and that their strength lies in their unity.’’