"I appeal again to all the political leaders, so that justice and peace prevail," he said in his weekly address to the faithful gathered in St. Peter's Square.
"I am deeply disturbed by the current world situation, in which, despite the tools available to the international community, it is difficult to agree on a common action in favour of peace in Syria and other regions of the world," he said.
Last Sunday, the pope denounced a reported gas attack in Syria as an unjustifiable use of "instruments of extermination".
The United States, France and Britain fired dozens of missiles early Saturday to strike at Syria's chemical weapons program -- the biggest intervention yet by Western countries against Syria, which is backed by Russia and Iran.