Pope Francis continued his press for peace in Syria on Sunday, using his traditional noontime Angelus address to say it’s “unacceptable that so many unarmed persons, including many children, have to pay the price of the conflict.”

“News of victims of civil war continues to arrive from Syria,” the pontiff said, “in particular from Aleppo.”

Aleppo is at the center of a battle between rebels and government forces. The rebels have been fighting to break a government siege on rebel-held neighborhoods, where the U.N. says 300,000 people are trapped.

Francis said the victims of the Syrian conflict are paying “the price of a closure of hearts, and a lack of will for peace by the powerful.”

“We’re close in prayer and solidarity to our Syrian brothers and sisters,” he said, “and we entrust them to the maternal protection of the Virgin Mary.”

Francis then asked the crowd in St. Peter’s Square to join him in a moment of silence followed by reciting the Hail Mary on behalf of Syria.

Since his election to the papacy, the violence in Syria has been a recurrent theme for Francis.

In September 2013, when the U.S. and other major Western powers appeared to be on the brink of using military force in Syria to dislodge the regime of President Bashar Al-Assad, Francis staged a special penitential liturgy in St. Peter’s Square to pray for peace, and criticized the idea of widening the conflict at almost every turn.

The pontiff’s efforts were later credited by Russian President Vladimir Putin with helping to prevent such a Western strike in the country.

On June 1 of this year, Francis asked children from around the world to use the International Day for the Protection of Children as a special day of prayer for the young people in Syria affected by the violent conflict, which broke out in 2011.

In early July, Francis released a video appeal for peace in Syria, complaining that the countries talking about bringing peace to the conflict-torn nation are also the ones supplying it with weapons.

He said that “peace in Syria is possible,” but that the only way to achieve it is through a political solution. In the video, the pontiff also gave his full support to the local Christian communities in Syria “for the discrimination they have to bear.”

An estimated 400,000 people have been killed in the five-year long conflict and millions have been displaced, “forced to survive under bombs or to find escape routes to other countries or areas of Syria that are less war-torn,” Francis said in the video.

The pontiff has also become a champion for refugees fleeing the violence in Syria, famously bringing 12 such Syrians back to Rome with him aboard the papal plane after a day trip to the Greek island of Lesbos in April.