"This administration has acted recklessly without care or consideration of the dire consequences of the US attack on Syria without waiting for the collection of evidence from the scene of the chemical poisoning," The Hill magazine quoted Ms Gabbard as saying on Thursday.
"It angers and saddens me that President Trump has taken the advice of war hawks and escalated our illegal regime change war to overthrow the Syrian government.
"This escalation is short-sighted and will lead to more dead civilians, more refugees, the strengthening of Al Qaeda and other terrorists, and a possible nuclear war between the US and Russia," she added.
Ms Gabbard's comments came after US warships on Thursday night launched 59 Tomahawk cruise missiles at a military airfield in Syria.
In February, Ms Gabbard stirred controversy after she made a trip to Syria and met Syrian President Bashar al-Assad, reports the magazine.
The Hawaii Democrat has insisted that the meetings were not planned and focused on peace efforts in the war-torn country.
Ms Gabbard released a separate statement ahead of the attacks on Thursday calling for an investigation into the chemical weapons attack in Syria and the eventual prosecution of Assad in the International Criminal Court.