Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

KRAKOW, Poland — Pope Francis declared that "the world is at war" on Wednesday, a day after two knife-wielding attackers linked with ISIS stormed a French church and slit the throat of a priest.

The pope made the comments on a flight between Rome and the Polish city of Krakow, where he was set to join hundreds of thousands of young pilgrims attending World Youth Day.

"The world is at war because it has lost peace," he told reporters. "This is war. The world has been at war for a while now ... We had the war of 1914, then the war in 1939-45, and now this one."

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

His comments come after a spate of ISIS-linked attacks across Europe in recent weeks — but he was clear not to describe the conflict along sectarian lines.

He said this was "not an organic war, perhaps. It’s organized, but not organic. But it’s war." He said the conflict was not "a religious war," adding that "all religions preach peace — it’s the others who want war."

Tuesday's attack saw two assailants armed with knives storm a church in Saint-Etienne-du-Rouvray and cut the throat of 85-year-old Father Jacques Hamel. Officials said the two attackers shouted "Allahu Akbar" before being shot dead by security forces.

French President Francois Hollande blamed the "cowardly acts" on ISIS-linked terrorists.

Jacques Hamel, who was killed Tuesday, celebrates Mass in June in the church of Saint-Etienne-du-Rouvray, Normandy. HO / AFP - Getty Images

Pope Francis said Hollande had called him to express his condolences. "I want to thank all of those who offered their sympathy, especially France’s president, who talked to me over the phone like a brother," he said.

He also referenced ISIS' other victims — many of whom are Muslims.

"This priest, who died as he was leading churchgoers to prayer, is one [victim]," he said. "But how many Christians, how many innocent children [have died]?"

The attack came before World Youth Day, one of the biggest catholic gatherings in the world. Polish authorities introduced exceptional security measures to protect the up to 2 million young pilgrims expected to descend on Krakow.

Around 20,000 Polish police and military personnel have been deployed across the city. Pilgrims will be asked to go through mobile X-rays and metal detectors at railway and bus stations.

Dogs trained to detect explosives will also be used. Gas tankers and large trucks had been barred from entering the city, and drones and any other "unauthorized flying objects" will be banned over a 65-mile zone above Krakow.