The US president met with his military leaders in Washington on Monday night to discuss the response to the "horrible attack" on Douma, saying a decision would be made "tonight or very shortly thereafter".
Fielding questions at the White House, Trump press secretary Sarah Sanders said it would be "outrageous" to say that Trump's recent announcement that he intends to remove all USA forces from Syria in the coming months had emboldened Assad.
President Donald Trump said on Monday that he and USA military officials were reviewing a U.S. response to the chemical weapons attack in Syria over the weekend and promised a forceful decision as early as Monday night.
"On the eve of potential United States and French strikes against Assad in response to the Douma gas attack, it is likely the Israelis already had the intention to strike at the T-4 base, and timed their attack to maximise the destruction they could inflict on Iranian forces", he told AFP.
"Without the support of Russian Federation, I do not believe Assad would still be in office", Republican Senator Susan Collins of Maine said, adding that she hopes the president will turn up the heat on Russian Federation over this attack.
"We received many patients who suffered from symptoms compatible with exposure to chlorine gas, high concentration chlorine gas", said Dr. Ahmad Tarakji of the Syrian-American Medical Society.
On April 7, 2017, nearly exactly a year ago, Trump ordered the US Navy to target a Syrian airbase with cruise missiles in the wake of a similar attack that the United Nations chemical weapons watchdog OPCW later pinned on Assad's regime.
At the time of the weekend attack in Douma, Syrian government forces and their allies were in the midst of clearing the last pocket of rebel resistance in the eastern Ghouta region, where the town is located.
Pro-government fighters reached a deal with the rebels controlling Douma in order to start evacuating people from the area.
Russian Federation and Syria have blamed Israel for an attack on a Syrian military airport on Monday that reportedly killed at least 14 people.
"These attacks took place either with Russia's tacit or explicit agreement, or despite its military presence on the ground", said French Ambassador Francois Delattre.
The situation has "gone beyond the scope of what was acceptable even during the Cold War", he said. Framing the discussion, UN Special Envoy to Syria noted that the body has been "unable to independently verify" the incident. He said an escalation of the conflict could have "unimaginable consequences".
British Prime Minister Teresa May called the attack "barbaric", saying during a visit to Denmark that "If they are found to be responsible, the regime and its backers, including Russian Federation, must be held to account". The government of President Bashar Assad has denied using poison gas.
So, how likely is it that President Trump will respond with tougher action against Russian Federation and Syrian President Assad this time? An attack with chlorine, which can be used as a weapon but is not outright banned by the treaty, could raise precedent issues, as there have been numerous recent allegations of chlorine attacks in Syria that have drawn no response from the Trump administration.
But Russia blocked several similar resolutions in the past, and Nebenzya hinted that the latest one - which he called "unacceptable" - would meet the same fate. The use of chemicals was a desperate move to force the militants to concede after talks had broken down, she said.
September 14, 2013: Then-U.S. Secretary of State John Kerry and Lavrov reach a deal that calls for the removal or destruction of Syria's chemical weapons by mid-2014. "The global community must not let this happen".