Syrian President Bashar al-Assad said Tuesday the cessation of hostilities in his country's five-year war is a "glimmer of hope."
In a German television interview, Assad said his government will do its part to make the truce work.
U.S. Secretary of State John Kerry called the next few days "critical" in building momentum toward the goal of de-escalating the Syrian conflict.
He spoke to reporters Monday evening in Washington as Syria entered its fourth day under a cessation of hostilities that includes pro-government fighters and opposition forces, but not Islamic State militants or those from al-Qaida-linked Jabhat al-Nusra.
Kerry said he and Russian Foreign Minister Sergei Lavrov agree there have been a number of violations since the truce began Saturday, but that they do not want to litigate them publicly. Instead, they will rely on a task force led by their two countries to investigate every reported violation and promote compliance with the halt in fighting.