"We are meeting with our military," the President said about this latest attack, promising "we'll be making some major decisions over the n next 24 to 48 hours."
"We're talking about humanity," Mr. Trump said. "It can't be allowed to happen."
The President also again sent a strong message to Moscow, which has been accused of allowing Syria to use chemical weapons in the past.
"If it's Russia, if it's Syria, if it's Iran - if it's all of them together, we'll figure it out," the President said.
Mr. Trump was asked directly if Russian leader Vladimir Putin bears responsibility for the attack.
"He may," the President said.
Mr. Trump, who has gone out of his way at times to avoid direct criticism of Russia and Putin, using a weekend tweet to point the finger directly at Moscow.
"President Putin, Russia and Iran are responsible for backing Animal Assad," Mr. Trump said of the Syrian leader.
On Capitol Hill, members of both parties denounced the latest chemical attack.
"The administration must now make Assad, Putin and Iran pay a significant price for continuing to kill innocent civilians in Syria," said Sen. Bob Corker (R-TN).
"Russia’s willful intransigence allows the Assad regime to commit acts of unspeakable terror on their own citizens," said Rep. Susan Brooks (R-IN).
There were other major foreign policy items discussed by the President in his photo op with reporters before Monday's Cabinet meeting, as Mr. Trump said planning continues on a summit meeting with North Korean leader Kim Jong Un.