Syrian activists, rescuers and medics claimed that a poison gas attack was launched against a rebel-held town near the capital. They say at least 40 people were killed in the attack in the town of Douma, which occurred Saturday night. Now, rebels in the area are reportedly willing to retreat.

Syrian government forces are being accused of mounting the attack. Although both Syria and the Russian military are rejecting such claims, other countries including the United States, Turkey, and Brittain have indicated that Syria may be responsible.

President Donald J. Trump sent out a tweet targeting Bashar Hafez al-Assad, the President of Syria.

He wrote: “Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world.”

He also dubbed the Syrian president “Animal Assad,” said the attack was “another humanitarian disaster” and called it “sick.”

The Associated Press reports that Turkey said there was “strong suspicion” that the Syrian regime used chemical weapons.

The Turkish statement said Syrian President Bashar Assad’s regime has “once again ignored” international agreements banning chemical weapons. It called on the international community to prevent, stop and punish such attacks, calling them an indiscriminate “crime against humanity.”

The AP also reports that Britain’s foreign secretary, Boris Johnson says the Assad’s forces have used poison gas in at least four attacks since 2014, and said reports of the latest deadly chemical weapons attack in Syria are “deeply disturbing.”

Johnson warned that Russia must not try to block an international investigation and that Britain backs an inquiry by the Organization for the Prohibition of Chemical Weapons.

Johnson says “those responsible for the use of chemical weapons have lost all moral integrity and must be held to account.”

Meanwhile, Syrian state media says rebels will release their last foothold in the eastern Ghouta and withdraw to north Syria.

From the AP: The SANA news agency says the Army of Islam group agreed Sunday to leave Douma, three days after the government resumed its assault on the besieged town. It says tens of buses have been sent to the town to pick up prisoners freed by the rebel group and to transport rebel fighters to opposition-held territory in north Syria.

The development comes hours after unconfirmed reports by first responders that the government had used chemical weapons against the town, asphyxiating at least 40 people.