PARIS — The two most vocal advocates of an international response to a chemical weapons attack in Syria teamed up on Saturday when Secretary of State John Kerry and his French counterpart made an unusual joint appeal for military action.

“France and the United States stand together,” said Laurent Fabius, the French foreign minister, who argued that a punishing military strike was needed to redraw the red line against the use of chemical weapons.

Mr. Kerry reached back to President John F. Kennedy’s meetings with President Charles de Gaulle and sought to touch a chord with wary Europeans over the need to stand up to the “slaughter” of civilians by delivering much of his presentation in fluent French.

France has displaced Britain as the United States’ main military ally if force is to be used against the Syrian government.