Stefano Rellandini / Reuters Pope Francis greets Catholic faithful during his arrival at Copacabana beach in Rio de Janeiro, July 25, 2013.

Update, Sept. 7, 3:37pm EST: Pope Francis spoke out this evening in St. Peter’s Square against an attack in Syria. For the full story, click here.

Pope Francis has written a letter to Russian President Vladimir Putin, host of the G-20 summit that President Obama is attending, urging world leaders to oppose a military intervention in Syria.

“To the leaders present, to each and every one, I make a heartfelt appeal for them to help find ways to overcome the conflicting positions and to lay aside the futile pursuit of a military solution,” the Pope urged. “Rather, let there be a renewed commitment to seek, with courage and determination, a peaceful solution through dialogue and negotiation of the parties, unanimously supported by the international community.”

(WATCH LIVE: Pope Francis’s Vigil for Peace in Syria)

The move is the latest in a series of efforts by the Holy See to prevent military action in the already civil-war torn region. On Sunday, the Pope declared in his Angelus teaching that Saturday Sept. 7 would be a day of fasting and prayer for peace in Syria. The prayer rally will take place in St. Peter’s Square from 7 p.m. to midnight, on the vigil of the birth of Mary, the Queen of Peace. “Let us ask Mary to help us to respond to violence, to conflict and to war, with the power of dialogue, reconciliation and love,” the Pope asked people around the world. “She is our mother: may she help us to find peace; all of us are her children!”

Next Pope Francis took his views on Syria to Twitter. On Monday he tweeted, “War never again! Never again war!” and “How much suffering, how much devastation, how much pain has the use of arms carried in its wake.” On Tuesday, he tweeted “We want in our society, torn apart by divisions and conflict, that peace break out!” and “With utmost firmness I condemn the use of chemical weapons.” Today his social media message was, “With all my strength, I ask each party in the conflict not to close themselves in solely on their own interests. #prayforpeace.”

Cardinal Dolan and leaders of the United States Conference of Catholic Bishops followed the Pope’s lead and wrote to every member of Congress today urging them to vote against military intervention in Syria. Yesterday the USCCB also wrote to President Obama, reminding him that the Pope and Middle Eastern Bishops “have made it clear that a military attack will be counterproductive, will exacerbate an already deadly situation, and will have unintended negative consequences.” Dolan also asked Catholics to urge their representatives in Washington to vote against a military strike.

The Vatican, which almost always stops short of taking sides in international issues, historically holds to just war theory, which requires a military defense meet a set of strict qualifications, including that “the damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain,” “all other means of putting an end to it must have been shown to be impractical or ineffective,” and “the use of arms must not produce evils and disorders graver than the evil to be eliminated.”

Pope Francis’ response to Syria is in line with how his predecessors handled international conflicts. Pope Benedict XVI expressed concerns over the military intervention in Libya. Pope John Paul II continually and strongly spoke out against the US-led war in Iraq. The US and the Vatican squared off during the 1989 Panama invasion when dictator Manuel Noriega took refuge in the Vatican embassy.

U.S. seals tried to blast Noriega out with deafening levels of rock music and only stopped the “rock-‘n’-roll offensive,” as TIME called it, after the Vatican complained to President George HW Bush. Pope John Paul II kept quiet on the crisis, and left it to the hands of Vatican officials.