CHICAGO: A key Nato summit, gathering more than 50 world leaders, opened in Chicago on Sunday with a minute's silence for all those who have fallen in combat around the world.

Led by Nato chief Anders Fogh Rasmussen and US President Barack Obama, the summit leaders stood and bowed their heads as a uniformed US bugler played “Taps.”

Rasmussen opened the two-day talks saying “our deepest sympathies go to the families and loved ones of all those who made sacrifices.”

Addressing the themes of the summit, he vowed to complete the transition to Afghan security by 2014.

He also stressed the need to embrace “a renewed culture of cooperation”vowing that “together we will make our partnerships deeper, broader and stronger.”

Obama trumpeted that “for over 65 years our alliance has been the bedrock of our common security, our freedom and our prosperity.”

”And though the times may have changed, the fundamental reason for our alliance has not,” he said, adding that “in good times and in bad our alliance has endured, in fact it has thrived.”

Outside, far from the waterfront convention center where the summit was being held, thousands of protesters gathered demanding an end to costly and destructive wars.