France and the United States on Thursday urged Russia to exert pressure on Syria to implement a resolution that the United Nations passed last month for a 30-day ceasefire in the war-torn nation.

Presidents Emmanuel Macron and Donald Trump spoke on telephone to discuss the situation in Syria, France’s Elysee Palace said in a statement on Friday. Macron said France would have a “firm response” if chemical weapons are used to kill civilians in Syria. “France and the United States will not tolerate impunity,” the statement said.

The presidents agreed to work together “to allow the cessation of hostilities, the delivery of humanitarian aid and the evacuation of the wounded and sick”, the statement said. They agreed that Russia needed to “unambiguously exert maximum pressure on the regime in Damascus” to make it abide by the ceasefire agreement.

On February 24, the UN Security Council approved the month-long ceasefire across Syria so humanitarian aid can reach people in the conflict zone. The ceasefire was ordered after Ghouta was continuously bombarded by airstrikes for over a week, leaving at least 520 people dead, many of them children. At least 2,500 people were injured in the strikes before the resolution.

However, Syrian President Bashar al-Assad’s forces continued to launch fresh attacks – both on the ground and from air – against rebel groups in eastern Ghouta, even after the resolution. Russian President Vladimir Putin blamed “extremist forces” for the continuing violence.