After discussions with Mr. Netanyahu, Mr. Kerry left Jerusalem for Paris, where he planned to meet on Monday with Laurent Fabius, the French foreign minister; William Hague, the British foreign secretary; and Ahmet Davutoglu, the Turkish foreign minister. Mr. Kerry also was scheduled to meet here separately with Saud al-Faisal, the Saudi foreign minister.

France, Britain, Turkey and Saudi Arabia have been vociferous critics of President Bashar al-Assad of Syria and supporters of the Syrian opposition.

Many allied officials now wonder how to strengthen the Syrian opposition militarily and shift the momentum on the battlefield since the United States has pulled back from a plan for military strikes, which were intended not only to punish the regime but to “degrade” some of Mr. Assad’s forces.

France and Britain are also permanent members of the United Nations Security Council.

Under the Geneva pact, the terms of the accord are to be included in a resolution under Chapter VII of the United Nations Charter, which would authorize punitive measures if Syria does not comply.

While Russia, another permanent member of the Council with veto power, would be likely to block any Security Council endorsement of a military strike, Mr. Kerry said the United States remains prepared to launch a unilateral strike if Syria fails to meet its commitments.

“This will only be as effective as its implementation will be, and President Obama has made it clear that to accomplish that, the threat of force remains,” Mr. Kerry said. “The threat of force is real.”

Speaking on TF1 channel on Sunday, President François Hollande of France made a similar point, emphasizing that the military option “should remain on the table.”