April 8 (UPI) -- Amid the re-engaged siege of Douma, a town in the Damascus suburb of Eastern Ghouta, forces loyal to Syrian President Bashar al-Assad launched a gas attack that killed dozens of civilians, activist and activist-sympathetic groups reported this weekend.
Ghouta Media Center and Syria Civil Defense, a volunteer rescue group, reported death tolls ranging from 40 to 75, saying at least one Assad-allied helicopter dropped a barrel bomb of chemicals that left civilians, including children, suffocating to death.
The Syrian American Medical Society, a nonprofit group of healthcare workers in Syria, said 500 people, mostly women and children, sought treatment at Douma healthcare facilities for symptoms consistent with a gas attack.
"Patients have shown signs of respiratory distress, central cyanosis, excessive oral foaming, corneal burns, and the emission of chlorine-like odor," the group said, adding that six people died at a medical center.
The Syrian government and the allied Russian Foreign Ministry have denied reports of the chemical attacks.
"We strongly deny these claims and announce our readiness to send Russian experts in radiation, chemical and biological defense to Douma after its liberation from terrorists to gather evidence, which would prove that the allegations on the chemical weapons use were staged," Maj. Gen. Yuri Yevtushenko, of the Russian Center for Syria reconciliation, said in a statement.
The enclave of Douma, one of the last areas of rebel control around Damascus, has been a flashpoint for violence late this week, following the start of ceasefire and evacuation negotiations about two weeks ago. The Syrian government said thousands of rebels and their families have evacuated the area since March, some on government-coordinated buses, but other members of the Jaish al-Islam resistance group remain in the area.
Sunday afternoon, Great Britain's United Nations office said on Twitter that it joined the U.S., Kuwait and other nations in requesting the U.N. Security Council hold an emergency meeting Monday to discuss reports of the chemical attack.
U.S. State Department spokeswoman Heather Nauert said her agency was continuing "to closely follow" reports of the attack. She said Russia was violating its U.N. commitments by supporting the Assad government.
"These reports, if confirmed, are horrifying and demand an immediate response by the international community," Nauert said. "The United States continues to use all efforts available to hold those who use chemical weapons, in Syria and otherwise, accountable."
U.S. President Donald Trump said on Twitter on Sunday the area of the attack was on "lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President [Vladimir] Putin, Russia and Iran are responsible for backing Animal Assad."
Trump ordered a missile attack on a Syrian airbase last April after a suspected Assad-backed chemical attack killed and injured hundreds of people.