"There is no ‘Plan B,’ there is only this critical moment where, somehow, Russia and the United States agreed to ceasing of hostilities. Beyond that, they have no plan," Jahshan said.
On February 23, the United States and Russia reached an agreement to implement a ceasefire in Syria, to ensure humanitarian aid flows and take a tangible step toward a political resolution of the five-year-old conflict.
During testimony to the US Congress last week, Secretary of State John Kerry said that, if the ceasefire failed, the United States would seek a "Plan B" in Syria, which could include partitioning the country.
"I don’t see any kind of Republican or Democrat who is committed to pursue the same logic that led to this ceasefire," he warned.
Given the 2016 presidential election cycle, it will "take a long time before the parties regroup…to resume where we left off," he added.
The cessation of hostilities went into effect on Saturday, following the passage of resolution 2268 by the UN Security Council. The ceasefire applies to all fighting parties in Syria, except the Islamic State, Nusra Front and other groups designated as terrorist by the United Nations.
According to reports, some parties on the ground in Syria have already reported ceasefire violations.