"War never again! Never again war!" Francis wrote on the micro-blogging website Twitter.
The Pope on Sunday deplored the suspected use of chemical weapons in Syria at the weekly papal appearance in St. Peter's Square.
"My heart is deeply wounded by what is happening in Syria and anguished by the dramatic developments," the Pope said.
He referred to the possible military intervention by the US and France to punish the Syrian government over the alleged chemical weapons attack against civilians in Damascus last month.
"With utmost firmness, I condemn the use of chemical weapons. I tell you that those terrible images from recent days are burned into my mind and heart," the Pope said. Never has the use of violence brought peace in its wake. War begets war, violence begets violence, he added.
Pope Francis: "War never again! Never again war!"
"I exhort the international community to make every effort in order to promote clear proposals for peace in that country without further delay, a peace based on dialogue and negotiation, for the good of the entire Syrian people," Pope concluded.
A top Vatican official on Monday said a military attack on Syria by western powers could cause "a war of global dimensions".
"The way to solve Syria's problems cannot be that of armed intervention," Monsignor Mario Toso, head of the Vatican's justice and peace council said.
"The only way forward is reason and initiatives based on dialogue and negotiation, which is possible if there is mutual respect and love," he added.