Shortly before the United Nations was due to discuss Syria, Macron said Moscow, a close ally of Syria's Bashar al-Assad's regime, had not done enough to permit relief efforts into the opposition-held Damascus suburb of eastern Ghouta.
More than 1,160 civilians have been killed since Russia-backed regime forces launched a brutal air and ground assault on Eastern Ghouta, the last stronghold of the armed opposition near the capital Damascus.
Reports on Sunday alleged that dozens of civilians had managed to flee Eastern Ghouta through a humanitarian corridor.
United States ambassador to the UN Nikki Hailey denounced the failure to implement the resolution, and said her country was drafting a new one with "no room for evasion".
State media showed footage of the Syrian Army and its allies break apart rebel lines over the weekend to surround the town of Douma.
Russia, which backs Syria's government in the civil war, and the United States, which has backed rebel forces seeking to topple Assad, met secretly in Jordan in June and announced a ceasefire in Syria's southwest a month later.
The Observatory, which tracks death tolls using a network of contacts inside Syria, said it had identified more than 350,000 of those killed, and the remainder were cases where it knew deaths had occurred but did not know the victims' names.
As the war approaches its eighth year, intense fighting continues in several areas, including eastern Ghouta near the capital Damascus and Afrin near the Turkish border. The expulsion of the rebels from eastern Ghouta would represent their biggest defeat since they lost their enclave in Aleppo in December 2016. "To our knowledge, not one critically sick or wounded person has yet been evacuated".
In rapid advances over the weekend, Syrian government forces split eastern Ghouta in two - a northern and southern part - then cut off the key towns of Douma and Harasta from the rest of the enclave, further squeezing residents living there.
People in Eastern Ghouta say they dread a similar fate.
Jaish al-Islam announced the move Monday, saying it had communicated with Russian Federation through the United Nations to reach the deal.
The UN Resolution 2401 that was unanimously passed by the Security Council on February 24 called on the parties to the Syrian conflict to stop all hostilities and adhere to a humanitarian pause across Syria in order to ensure the safe and unhindered delivery of humanitarian aid, as well as medical evacuation of those injured.
All three towns are controlled by Islamist rebel group Faylaq al-Rahman, which has repeatedly denied engaging in talks with the regime.
Mattis said that he was aware of reports of chlorine attacks on Eastern Ghouta but said that he did not have conclusive evidence that gas had been used.
The Britain-based Syrian Observatory for Human Rights monitoring group says an indiscriminate campaign of regime and Russian air strikes and shelling has killed some 1,100 civilians in rebel-held Eastern Ghouta over the past three weeks.