US Secretary of State John Kerry on Sunday warned the regime of President Bashar al-Assad and its allies including Russia against exploiting the fragile ceasefire in Syria for their own means.

"If the regime and its backers think they can test boundaries, diminish their compliance in certain areas, or act in ways that call into question their commitment to the cessation –- without serious consequences for the progress we have made -- they are mistaken," Kerry said after talks with his European allies in Paris.