Trump said he would partner with Jordan and other regional allies, including Egypt and Iraq, to address the problem.
Turkey set up a decontamination center at a border crossing in the province of Hatay following the attack, where the victims are initially treated before being moved to hospitals.
The Organisation for the Prohibition of Chemical Weapons (OPCW) said it was "seriously concerned" by reports of Tuesday's attack.
The death toll rose to 72 by Wednesday, including 20 children and 17 women.
"All the evidence I have seen suggests this was the Assad regime. using illegal weapons on their own people", Johnson said as he arrived for the aid conference. Speaking about Tuesday's gas attack, the White House condemned Assad but also lay blame on the Obama administration. Some blamed the government of Syrian President Bashar al Assad.
Robert Mardini, who oversees operations in the Middle East for the International Committee of the Red Cross said the situation was nothing short of catastrophic in Syria.
A Syrian opposition group said renewed airstrikes hit the town of Khan Sheikhoun a day after the attack, which the Trump administration and others have blamed on the government of President Bashar Assad, as well as his main patrons, Russian Federation and Iran.
In an interview with the AM Tampa Bay radio show, Senator Marco Rubio (R-FL) pointed out that the horrific gas attack ordered by Syrian President Bashar Al-Assad - in which dozens of children died, and the use of a nerve agent or other banned chemicals is suspected - took place after Secretary of State Rex Tillerson publicly acknowledged that his removal would no longer be an American priority. It's one of the worst attacks in the country's six-year civil war.
A UN-appointed fact-finding committee a year ago concluded that chemical weapons had been used by Syrian regime forces and opposition groups in 2014 and 2015.
Sen. Bob Casey of Pennsylvania calls a White House statement on the attack weak because it omits any mention of Russian President Vladimir Putin. "It was a great opportunity missed", Trump said. But Moscow has consistently blocked United Nations action on Syria but proven unable to contain Mr. Assad's bad behavior. "And we don't see it".
IBD/TIPP Poll: Trump Losing White Male Voter Support
The president's approval rating remained well underwater, with 56 percent of the respondents disapproving of his job performance. Just 25 percent say the healthcare bill he pitched with House Speaker Paul Ryan, R-Wis., would improve the nation's healthcare.
Casey and Minority Leader Chuck Schumer of NY say Trump is being undermined by the cloud of an ongoing investigation into possible Russian interference in the election.
Syria's deputy United Nations ambassador Mounzer Mounzer told the council his government categorically rejects "false claims and accusations" that the army used toxic chemicals against Syrian civilians in Khan Sheikhoun, saying they are being used "as human shields by armed terrorist groups". Britain and France on Wednesday renewed their call for Assad to leave power.
Hours before the U.N. Security Council meets over a resolution proposed by Washington, London and Paris on the attack, Guterres said: "We have been asking for accountability on the crimes that have been committed and I am confident the Security Council will live up to its responsibilities". We trained clinic staff and community health workers on how to respond to chemical attacks, and these health workers in turn taught people in their communities how to protect themselves from contamination.
The president released a statement Tuesday condemning the attack as "reprehensible".
It has always been clear that the Obama administration accepted that face-saving deal proffered by Russian Federation at a high cost to its own credibility and to US national interests.
Britain said he would be guilty of a war crime if it were proved that his government was responsible.
But Moscow, which holds a veto, defended its Damascus ally saying that while Syrian aircraft had carried out a strike, the chemicals were part of a "terrorist" stockpile of "toxic substances" that had been hit on the ground.
Damascus and Moscow have denied they were behind the attack.
Trump has not indicated how, or even whether, the USA might respond to the attack.