Over the course of Assad’s bloody crackdown on protesters and rebel fighters over the past 20 months, Russia and China have vetoed three tough sanctions resolutions at the U.N. Security Council that were intended to punish the Syrian government.

The United States has been trying to get Russian support for an international transition plan for Syria. At the State Department, Nuland called on Russia “to withdraw any residual support for the Assad regime, whether it’s material support, financial support.”

At the same time, she said, the Russians can “help us to identify people who might be willing, inside of Syria, to work on a transitional structure. . . . They have a lot of contacts in Syria.”

At least one anti-government activist appeared to scoff at the change in message from the Russian government on Thursday.

“ ‘Finally, you’re waking up to the truth?’ ” the activist, who uses the nom de guerre Majd al-Shami, said via Skype.