Pope Francis called on world leaders on Sunday to renew efforts to bring peace to Syria, saying he was deeply troubled by their failure to agree on a joint plan to end the bloodshed.

'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.

Earlier Syrian church leaders condemned the airstrikes as 'unjustified aggression' and a 'clear violation of the international laws'. 

The leaders of Syria's three major churches denied President Bashar al-Assad, who they see as a positive force for Syria's Christian minority, either owned or used chemical weapons. 

A statement signed by John X, the Greek Orthodox Patriach of Antioch and all the East, Ignatius Aphrem II, Syrian Orthodox Patriach of Antioch and all the East, and Jospeh Absi, Melike-Greek Catholic Patriach of Antioch, Alexandria and Jerusalem called on the United Nations' Security Council to 'play its natural role in bringing peace rather than contribute to escalation of wars'.

They also urged churches in the UK, US and France to 'fulfill their Christian duties' and 'condemn this aggression and to call their governments to commit to the protection of international peace'.