Washington (CNN) President Donald Trump said Monday he will make a decision as early as this evening on the US response to what he called an "atrocious" chemical weapons attack on civilians in Syria and warned that he will hold the responsible parties accountable.

"We cannot allow atrocities like that. Cannot allow it," Trump told reporters on Monday during a Cabinet meeting as he warned that "nothing's off the table." "If it's Russia, if it's Syria, if it's Iran, if it's all of them together, we'll figure it out and we'll know the answers quite soon."

Pressed on Russia's role in the suspected chemical weapons attack, Trump said Russian President Vladimir Putin -- who backs the Syrian regime -- "may" bear responsibility.

"He may. And if he does, it's gonna be very tough. Very tough," Trump said of the US response. "Everybody's gonna pay a price. He will and everybody will."

The Syrian government and Russia have vehemently denied involvement in the attack and accused rebels in Douma of fabricating the chemical attack claims in order to hinder the army's advances and provoke international military intervention.

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