"Let me be clear, the United States, President (Barack) Obama, myself, others are in full agreement that the end of the conflict in Syria requires a political solution. There is no military solution, we have no illusions about that," Kerry said after his meeting with UK Foreign Secretary William Hague.
"But a resolution to this has to come about because the parties are prepared to come and negotiate that political solution. A resolution will not be found on the battlefield, but at that negotiating table. But we have to get to that table," Kerry said.
"We're not talking about war. We are not going to war. We are not going to have people put at risk in that way. We are going to be able to hold Bashar al-Assad responsible without having troops on the ground," he told reporters.
The US has alleged that the nerve agent sarin was used by the Assad regime on August 21 and that at least 1,429 people were killed, including over 400 children, a charge denied by the Syrian government.
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Questioned about the strength of the evidence against Assad, Kerry invoked his past as a public prosecutor in Massachusetts to say that he had sent criminals down for life on less.
"The evidence is powerful and the question is, what are we going to do about it? I don't believe that we should shy from this moment. The risk of not acting is greater than the risk of acting," he said.
"Our bond is bigger than one vote, bigger than one moment in history. The relationship remains as relevant today as it has in the past," he said during a joint press conference with Hague.