The Pentagon denied any USA involvement, but analysts say Trump's remarks, which come exactly a year after he ordered a missile strike in response to a deadly sarin gas attack, suggets another assault is likely. Jaish al-Islam did not respond to requests for comment. They come at seminal junctures in the conflict, when Syrian government forces are on the verge of a significant strategic victory or advance against the alphabet soup of Salafi-jihadi groups that are operating in the country.
Russian Federation has repeatedly blocked efforts to hold Syria accountable both at the United Nations and OPCW.
However, two officials said Trump has been adamant about withdrawing USA forces from Syria, despite warnings about the consequences from Defense Secretary Jim Mattis and other military officials.
Graphic images showed people, including children, apparently dead and injured - some with some kind of spittle or foam in their mouths in makeshift medical centers.
A UN Security Council resolution failed to quell the fighting, and over the past month, more than 130,000 Syrians have left Eastern Ghouta as part of evacuation deals between rebels and government forces, the United Nations said.
The Kremlin warned on April 9 against jumping to conclusions, after Moscow said its experts had found no traces of chemical weapons.
As worldwide officials worked to try to confirm the chemical attack which happened late on Saturday in the town of Douma, Trump took the rare step of directly criticizing Russian President Vladimir Putin in connection with the incident.
In a joint statement, the White Helmets and the humanitarian group Syrian American Medical Society (SAMS) said 48 people were killed.
"We are ready, once Douma is freed from militants, to immediately send Russian specialists in radiation, chemical and biological defence to collect data that will confirm these claims are fabricated", he said, quoted by news agencies. Americans are desperately in the quest for legitimate intervention in Syria possibly for another strike against government targets.
If confirmed, the use of chemical weapons would be another instance of the banned substances alleged to have been used in Syria's brutal civil war.
"It is a matter of grave concern that chemical weapons continue to be used, especially on civilians", the European Union said in a statement.
A year ago, almost 100 people were killed in a strike on the northern town of Khan Sheikhoun that the United Nations has blamed on the Syrian air force.
Poland's foreign ministry has condemned the suspected use of chemical weapons in an attack on Saturday in the rebel-held Syrian city of Douma. Damascus denied it was behind the attack and has repeatedly denied it has any chemical weapons.
- Russian Federation casts a veto at the UN Security Council preventing the renewal of the mandate for the Joint Investigative Mechanism.
After a lull of a few days, government forces began bombarding Douma again on Friday. It was once one of the hubs of the 2011 Arab Spring-styled uprising against President Bashar Assad's government.
Eastern Ghouta was one of the first areas near Damascus to revolt in 2011. "Then you start getting a lot of people who are suffocating, and they smell of chlorine, and imagine after all that exhaustion you get this huge number of people, around 70, targeted while they were in bomb shelters".