The American leader met with his cabinet and vowed to make "major decisions" within the next 24 to 48 hours, amid mounting speculation about a United States military response.
In an impassioned speech at the U.N., Haley declared, "Only a monster does this".
"We can't let that happen".
Russian Federation vetoed a Western-backed resolution in November that would have extended the mandate of the joint UN-Organization for the Prohibition of Chemical Weapons body that had blamed the Syrian government and the Islamic State extremist group for using chemical weapons.
On Sunday, the National News Agency of Lebanon reported that Israeli surveillance aircraft had been hovering over the country's northeast, near the border with Syria, for three days. The strike took place after a suspected chemical weapons attack on the rebel-held town of Douma which, according to one Syrian aid organisation, killed at least 60 people.
Trump made the remark in the Cabinet Room of the White House during a meeting Monday evening with his top military leaders, including Defense Secretary Jim Mattis and the chairman of the Joint Chiefs of Staff, Gen. Joseph Dunford.
Rescuers and medics in Douma say more than 40 people died after a "poisonous chlorine gas attack" late Saturday in the last rebel-held pocket of Eastern Ghouta. The Pentagon denied in a statement that the US military had launched the missile strikes and would continue to "closely watch the situation".
As the fallout continued on Monday, Nikki Haley, the USA ambassador to the United Nations, told the urgent meeting that Washington was ready to "respond" to the attack regardless of whether the Security Council acted or not.
"History will record this as the moment when the Security Council either discharged its duty or demonstrated its utter and complete failure to protect the people of Syria", Haley said.
At a photo-taking session in the Pentagon on Monday, Mattis said "the first thing" to consider in how to respond was why chemical weapons are "still being used at all". "Here we are in a world where chemical weapons use is becoming normalized, from an Indonesian airport to an English village to the homes and hospitals of Syria". She alleged that such actions were consistent with Assad's "established pattern of chemical weapons use".
"That will give the United States and possibly France an excuse for military action". The mechanism, however, ceased to function in November 2017 after Russian Federation blocked the renewal of its mandate.
Both the Syrian government and its Russian backers deny responsibility for the attack.
The Russians are asserting that evidence is being manufactured to essentially frame the Syrian government for the chemical attack.
Syrian regime forces have waged an assault since February 18 on Ghouta, that has killed more than 1 700 civilians and left Islamist rebels cornered in their last holdout of Douma, Ghouta's largest town.
French President Emmanuel Macron was quick to engage with the White House, which announced that USA will be coordinating with France on a response, military or otherwise.
"The likeliest option is exactly what we saw before - an airstrike that the president puts forward as a so-called tough response but doesn't do very much to degrade Assad's forces or to punish him for his ongoing use of chemical weapons", said Jonah Blank, an analyst at RAND Corp.
Acting Secretary of State John Sullivan spoke by phone Monday with British Foreign Secretary Boris Johnson. "Signalling we want to remove our troops in no way degrades our ability to hold parties responsible", she said in response to a question.