VATICAN CITY (AP) — The Vatican is ramping up its opposition to threatened military strikes against Syria as it draws attention to Pope Francis' plans to host a day of fasting and prayer for peace this weekend.

The Vatican has invited all ambassadors accredited to the Holy See to attend a briefing Thursday on the pope's agenda for the four-hour vigil Saturday night in St. Peter's Square, and bishops' conferences from around the world have announced plans to host local versions of the vigil as well.

Even the Vatican's often dysfunctional bureaucracy seems to be on message with the initiative, Francis' first major foray into international diplomacy since being elected in March.

The No. 2 of the Vatican's justice and peace office warned earlier this week that military action in Syria could spark a world war. The head of its office for families wrote a letter to Catholics urging parents to offer their children an "austere and minimal lunch" Saturday to participate in Francis' fast. And the cardinal in charge of the Vatican's office for Eastern rite Catholics warned in an interview with the Vatican newspaper that Christian minorities in the region would suffer the most from any military intervention.

Francis himself on Wednesday urged Catholics and non-Catholics alike to participate in Saturday's vigil, telling more than 50,000 people gathered for his weekly general audience: "Let the cry for peace rise up across the Earth!"

In recent speeches, tweets and remarks, Francis has called for a negotiated settlement in Syria but has also condemned the use of chemical weapons.

"War never again! Never again war!" he tweeted earlier this week.

It's an anti-war exhortation that echoes those issued by popes past starting with Pope Pius XII in his 1951 Christmas radio message. Pope Paul VI uttered the same words at the United Nations in 1965 as the Vietnam War raged. Pope John Paul II repeated them in calls for peace in Bosnia and Iraq and Benedict XVI used the refrain during a 2011 peace meeting with religious leaders in the Umbrian hilltop town of Assisi.

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John Paul took his anti-war initiative a step further when, on the eve of the 2003 U.S.-led invasion of Iraq, he sent a personal envoy to U.S. President George W. Bush to try to dissuade him from starting war.

For Francis, whose namesake St. Francis of Assisi was known for his message of peace, Saturday's public vigil will be something of a test to see if his immense popular appeal translates into solid popular support for his anti-war initiative.

On Wednesday he urged Romans in particular to come to St. Peter's for the vigil, which will feature moments of silent prayer as well as remarks by Francis.

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