An estimated 60,000 anti-globalisation protesters have marched in the Venezuelan capital, Caracas, at start of the World Social Forum.
US anti-war activist Cindy Sheehan, who held a vigil outside US President George W. Bush's Texas ranch after her soldier son was killed in Iraq, led the flag-waving crowds shouting "No to the war."
"We need to stop the war in Iraq, we need to bring our troops home immediately," Sheehan said from a stage. "We need to see George Bush and the rest of them tried for crimes against humanity. We need justice for our children."
Many at the rally hailed Venezuelan President Hugo Chavez, a self-styled socialist revolutionary and critic of Washington, who has become a regional standard-bearer for left-wing and anti-US movements since allying himself with Cuba.
Colombian drummers, whistles and stilt-walkers brought a festive atmosphere to an event that has become a central forum for international debate on subjects as diverse as gay rights, anti-globalisation and global arms control.
"This is against conflict, against wars all over the world," said Marie Eve Rheault, from Quebec, Canada, who was helping hoist a peace dove fashioned from white sheets.
The sixth forum registered more than 67,000 participants at the start of the six-day event, which began in 2001 in Brazil as an alternative to the gathering of world leaders in Davos, Switzerland, but has since become part of a broader movement.
Newly arrived Ecuadorean Indians in traditional shawls sat among piles of their luggage at the start of the Caracas event while Brazilian students surveyed stalls offering Che Guevara T-shirts and watches and posters printed with Chavez's image.
