Pope Francis on Sunday invited people of all faiths to join him and the world's Catholics in a day of prayer and fasting on September 7 to end the bloody three-year internecine conflict in Syria.
Addressing tens of thousands of people who had gathered in St. Peter's Square, Francis issued a long, impassioned appeal for peace in Syria and across the Middle East, saying God and history would be the judge of those who promoted violence or prevented peace.
The pope condemned the use of chemical weapons, which Western powers say were clearly used by Syrian government forces, but added: "War, never again".
The United States and France are considering military action against Damascus in response to the chemical attack on August 21, which the US says killed more than a thousand people, but Francis urged the international community to make every effort to bring about peace based on "dialogue and negotiations".
"Violence never leads to peace, war leads to war, violence leads to violence," he said.
The pope asked the 1.2 billion Roman Catholics around the world to pray for peace in Syria and observe a day of prayer and fasting on Saturday.
Francis announced his initiative a day after a meeting of top Vatican officials on Syria. He said he would lead a special prayer service in St. Peter's Square on Saturday between 7 p.m. and midnight (1800-2300 GMT).
The pope invited other Christians, members of other religions and all "people of goodwill" to join the Catholic initiative in any way they saw fit.
The peace initiative is reminiscent of several made by the late Pope John Paul, including one in which he dispatched envoys to Iraq, the United States and European capitals in 2003 to try to avert war in Iraq.