France's Emmanuel Macron and U.S. President Donald Trump agreed on Friday to work together to implement a United Nations-backed ceasefire in Syria and called on Russia to exert its influence over Damascus, the Elysee Palace said in a statement.

Macron and Trump spoke by telephone to discuss the situation in Syria, and the enforcement of a ceasefire aimed at ending hostilities, opening access to humanitarian aid in eastern Ghouta and evacuating the wounded.

The two leaders agreed that Russia needed to "unambiguously exert maximum pressure on the regime in Damascus" for it to abide by the ceasefire, the statement said.

Macron also reiterated that France would have a "firm response" if it transpired chemical weapons led to the death of civilians in Syria.