Kerry joined his British counterpart William Hague during a London conference meant to drum up support for negotiations on Syria's future set to take place next month in Geneva, Switzerland.
In mid-October, the Syrian National Council, the formal government in exile, said it was wary of the prospects for any peace talks in Geneva.
So-called Geneva II talks, supported by the U.S. and Russian governments, are aimed at bringing rebels and the government together to hammer out a political settlement. Russian delegates were absent from the London meeting.
Kerry was quoted by The Daily Telegraph as saying talks were vital for the durability of Syria as a state.
"We believe that the state of war will simply lead to the implosion of the state of Syria," he said. "The only alternative to a negotiated settlement is continued if not increased killing."
Kerry said last week there can be "no military solution in Syria." A targeted strike was considered by the U.S. government after the nerve agent sarin was used as a weapon during conflict in Syria in August.
Syrian President Bashar Assad has clung to power despite civil war approaching its third year. British Foreign Secretary William Hague was quoted as saying the defiant president "has no role in a peaceful and democratic Syria."