US Secretary of State John Kerry said on Sunday military action cannot put an end to Syria's five-year conflict.
"In the end there is no military solution to the conflict," Kerry said in a televised statement, Reuters reported.
He appealed to both sides in Syria peace talks in Geneva to seize opportunity to make measurable progress despite an attack by Islamic State militants that killed dozens of people in the war-torn country on Sunday.
Kerry said the conflict could easily engulf the Middle East if no negotiated settlement was achieved. He also called for immediate steps to increase food aid and other humanitarian assistance to Syrians.
Syria's main opposition group met UN mediator Staffan de Mistura for the first time on Sunday, but the peace process ran straight into trouble after IS suicide bombers killed more than 60 people near the country's holy Shiite shrine.
The United Nations is aiming for six months of negotiations, first seeking a ceasefire, later working toward a political settlement to the civil war that has also killed over 250,000, driven more than 10 million from their homes and drawn in global powers.
