French President Francois Hollande on Tuesday described the hostage crisis in the northern part of his country as a "vile terrorist attack" on a religious institution.
He was speaking after two men were shot dead after taking several people as hostages in France's northern Normandy church on Tuesday.
The duo, armed with knives, took the people hostage in Saint-Étienne-du-Rouvray, reports The Guardian.
Reports suggest that five hostages were being held, and that a sixth escaped and raised the alarm.
Among the hostages were a priest, two nuns and two worshippers.
France's national police force has urged people not to cross the security cordon or take photos or videos of the scene in a tweet.
The incident comes under a fortnight after the Nice attack, where an Isis supporter drove a lorry into crowds celebrating Bastille Day which left 84 people dead and more than 300 injured.
Since the Islamic State's bombings and shootings in Paris last November, France has been on a state of high alert.