At least 40 people were killed and hundreds more were injured.
Speaking in the White House, Mr Trump said: "It was an atrocious attack, it was disgusting, you don't see things like that - as bad as the news is around the world, you just don't see those images".
Trump on Monday promised a decision on Syria within hours, although he did not say when a decision would be implemented.
Like the Russian envoy, Syria's ambassador to the UN, Bashar Jaafari, attacked the United States, its allies and UN humanitarian workers. "This is about humanity. and it can't be allowed to happen".
Also Tuesday, Russia vetoed a U.S. draft resolution at the UN Security Council that would have established an independent investigation into what happened in Douma.
Haley called out the Russian and Syrian governments, saying that "no civilized government would have anything to do with Assad's murderous regime".
"Repeating what Mr. Trump did in April of 2017 won't fix the chemical weapons problem in Syria", said Ford. "Because, as you know, they are claiming they didn't make the attack".
"So, we're looking at that very, very strongly and very seriously".
China today rejected the alleged use of chemical weapons in the Syrian town of Duma or another area of the planet, after supporting the development of an investigation to clarify the matter. She called Assad a "monster" incapable of remorse and said his Russian enablers were incapable of shame.
Speaking at a news conference on a trip to Denmark, Mrs May declared that "incidents like this can not be tolerated".
"If this is the responsibility of Assad's regime in Syria then it's yet another example of the brutality and brazen disregard for their people that they show".
"If they are found to be responsible, the regime and its backers, including Russian Federation, must be held to account".
The UN Security Council is due to vote on three draft resolutions on chemical weapons attacks in Syria on Tuesday, setting up a showdown between the United States and Russian Federation.
She declared: "This must stop".
Trump will be joined at the White House on Monday by John Bolton, who takes over as White House national security adviser.
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Mrs May replied: "We are clear that those responsible should be held to account".
Haley has been a vocal critic of Russia's actions in Syria.
The Trump administration has also asked the United Nations Security Council to authorize an independent inquiry into the attack. The U.S. threatened military action but later backed down. "I'm not going to get into specifics on intel matters and things that we may or may not do".
The U.S. launched several dozen Tomahawk cruise missiles at a Syrian air base past year after a chemical attack in the northern Syrian town of Khan Sheikhoun killed dozens of people.
Foreign Secretary Boris Johnson spoke to acting U.S. secretary of state John Sullivan and French foreign minister Jean-Yves Le Drian on Monday.
Trump is faced again with the choice of conducting a limited strike that might not even deter Assad from future chemical attacks or a wider response that risks drawing the USA deeper into a global conflict. His statement comes nearly exactly a year after he fired 59 Tomahawk missiles at a Syrian airbase in response to a chemical weapons attack against civilians.
While the Syrian presidency of the conference is due to the automatic rotation of member states, Neuer argued that UN Secretary-General Antonio Guterres was nonetheless obliged to speak out "when a UN committee makes obscene decisions which only cast a shadow on the reputation of the UN as a whole".
The politician, who spoke on condition of anonymity because he was not authorized to speak about secret military movements, said the atmosphere and USA statements hint at a possible strike, "but there are no indications on the ground so far".
Initial US assessments have been unable to determine conclusively what materials were used in the attack and could not say with certainty that Assad's forces were behind it.
"Syria is a tragic example of the cost of inaction".
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And any new action raises the risk of open conflict with Russian Federation which, like Iran, has deployed forces to defend Assad's regime.
Russia, Iran and Syria have blamed Israel for Monday's attack on the T4 air base in the central province of Homs that a Syria war monitor said killed 14 people, including Iranians.
They quoted a doctor and an ambulance driver who both reportedly said they had not dealt with anyone showing symptoms of chemical poisoning.
Lord Hague, who was foreign secretary when then prime minister David Cameron lost a Commons vote he wanted to back action in Syria, said the aftermath of the defeat left the United Kingdom "enfeebled spectators of one of the most destructive conflagrations of our time". Scores dead, including children.