Kerry, as he has done for the past week, tried to walk a fine line between sounding a battle cry in Syria and claiming the United States was "not going to war," a reflection of how difficult the Obama administration is finding it to sell an attack on Syria.
When arguing for the need to strike, Kerry compared the chemical weapons attacks to the Holocaust, which killed more than 6 million, and the Rwandan genocide, during which almost 1 million people died in the 1990s.
"If one party believes he can rub out countless numbers of his own citizens with chemical weapons, he will never get to the negotiation table," Kerry argued. "A resolution will never get done on the battlefield. It will be done at the negotiating table. But we have to get to that table."
But at the same time, he also tried to downplay the scope of the U.S. plans, saying an attack was not an act of war.
"We're not talking about war. We are not going to war," Kerry said. "We are going to be able to hold Bashar Assad accountable, in a very limited, very targeted, very short-term effort that degrades his capacity to deliver chemical weapons without assuming responsibility for Syria's Civil War."
A small group of protesters outside the British foreign office disagreed, holding up signs that said, "Hands Off Syria."
"One, two, three four," they chanted, "we don't want another war."
After the news conference, Kerry left for Washington to lobby Congress to authorize the military strike in Syria.