The Pope spoke to reporters on his flight to Poland for World Youth Day

The world is at war, but it is not a war of religions, Pope Francis has said as he traveled to Poland on his first visit to Central and Eastern Europe in the shadow of the slaying of a priest in France.

The killing of an 85-year-old priest in a Normandy church on Tuesday added to security fears surrounding Francis’s five-day visit for the World Youth Day celebrations, which were already high due to a string of violent attacks in France and Germany. Polish officials say they have deployed tens of thousands of security officials to cover the event.

Francis spoke to reporters on the papal plane en route from Rome to Poland. Asked about the slaying of the priest, Francis replied: “It’s war, we don’t have to be afraid to say this.”

After greeting reporters on his papal plane he returned to the topic to clarify that when he speaks of war, he is speaking of “a war of interests, for money, resources. … I am not speaking of a war of religions. Religions don’t want war. The others want war.”

Upon arrival at Kraków airport a pensive Francis was greeted by Poland’s President Andrzej Duda, First Lady Agata Kornhauser-Duda and other state officials, and hundreds of faithful who had waited for hours to see him.

The Polish army band played the anthems of the Vatican and of Poland.

“Let’s live WYD in Kraków together!” the Pontiff tweeted before departing from Rome for Krakow, southern Poland, on Wednesday afternoon.

Just hours before Francis’s arrival, groups of cheerful young pilgrims were seen in the streets of Kraków.

Relics of St Mary Magdalene came to the church from France, for the duration of World Youth Day, and were displayed in a case by the altar.

“Their presence helps us concentrate on our prayers and brings us closer to God,” said Nounella Blanchedent, 22, from the French Caribbean island of Guadeloupe.

She was one of the volunteers helping with security and logistics at the packed St Casimir Church, where a Mass was being celebrated in French for pilgrims from France, Belgium and other countries.

Folk dancers await the Pope's arrival at the military airport in Kraków (AP)

A group of folk dancers awaits the Pope’s arrival at the military airport in Kraków (AP)

The sense of expectation was apparent in sunny Kraków on Wednesday with papal white-and-yellow flags and images of Francis and John Paul II decorating the streets. Stages were put up at many locations for concerts and other activities that are being held by and for the pilgrims in Krakow.

There was a heavy presence of police and other security forces across the city, as crowds were increasing everywhere.

“I have never seen so many people in Krakow, it’s difficult to move around even though offices have closed [for the event] and many people have left the city,” said Anna Gazda, 43, owner of a souvenir shop.

Meanwhile, Cardinal Pietro Parolin, Vatican secretary of state, sent a message of condolence to Archbishop Dominique Lebrun of Rouen after the killing of Fr Hamel, Catholic News Service reports. The cardinal said Pope Francis was “particularly upset that this act of violence took place in a church during Mass, the liturgical act that implores God’s peace for the world.”

In the latest event of violence, the cardinal said, the Pope prayed God would “inspire in all thoughts of reconciliation and brotherhood.”

Chaldean Archbishop Bashar Warda of Irbil, Iraq, was another church leader in Krakow for World Youth Day. He told Catholic News Service the attack in France reminded him of the 2010 massacred in Baghdad’s Church of Our Lady of Deliverance “when they held the people inside the church” during Sunday evening Mass “and killed two priests and then started killing the rest.” A total of 48 people were killed and more than 100 were injured.

“This is the sort of world we are living in,” Archbishop Warda said. “We pray for the priest and everyone who was shocked and horrified.”

At the same time, “we pray for all of ISIS so they could really wake up and know the God of mercy,” he said. “We know that it is going to be harder and harder because the more you push them, they come up with more terrifying stories and events.”

“It’s shocking, it’s sad, really sad” to know they could “enter a church, a place of prayer” and commit such violence, the archbishop said. “Imagine you enter a mosque and start killing people — but that’s ISIS. That’s the way they act. Unfortunately this is the way they’ve been trained.”

Archbishop Joseph E. Kurtz of Louisville, Kentucky, president of the U.S. Conference of Catholic Bishops, expressed gratitude for “the unforgettable witness of the faithful” in the church attack.

“Jesus calls us to be sisters and brothers, to strive to care for one another, and always to reject the evil that seeks to divide us,” the archbishop wrote in a July 26 statement.