Updated

Tens of thousands of people have answered Pope Francis' call and massed in St. Peter's Square for a 4-hour prayer vigil for peace in Syria.

It was believed to be one of the largest rallies in the West against proposed U.S.-led military action against Syria's ruling regime following the Aug. 21 chemical weapons attack near Damascus.

Rainbow "Peace" flags fluttered in the evening breeze and religious leaders from a variety of Christian and non-Christian denominations joined cardinals, politicians and ordinary folk for the evening of prayer, hymns and meditation presided over by Francis.

The pope entered the square from the basilica steps, foregoing his usual drive through in his open car — an indication of the sobriety of the evening, which capped a day of fasting for the pontiff.