Mr Kerry, chairman of the Senate foreign relations committee, met with the president, Bashar Assad, on Saturday, his second such meeting in as many months. No details were made public about the substance of their three-hour discussion and state-run newspapers carried no news of the visit, facts that Syrian analysts said indicated the seriousness of the talks.

“John Kerry is an important link between Washington and Damascus, and with US-Syrian relations under strain, his presence will help to keep that connection open,” said Mazen Bilal, an independent Syrian journalist and political commentator. “Kerry has been a strong advocate of dialogue and is prepared to listen to Syria’s point of view. His visit will help calm the situation.”