The State Department on Monday said the symptoms of the alleged chemical attack in Douma, Syria, over the weekend were consistent with a nerve agent.

“The chemical weapons attack took place in an area of Syrian regime operations, Duma, where regime forces are attempting to dislodge the opposition. Syrian regime forces and their allies are denying international monitors access to the Duma area,” the State Department told Reuters.

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“The Duma victims’ symptoms, reported by credible medical professionals and visible in social media photos and video, are consistent with an asphyxiation agent and of a nerve agent of some type,” the department continued.

Dozens of civilians were reportedly killed on Saturday during the attack on the rebel-held city, roughly 10 kilometers northeast of the Syrian capital of Damascus.

The Syrian government has denied responsibility for the attack, but the U.S. and its international allies have laid blame on Damascus.

The Trump administration has also called out Russia and Iran for their support of Syrian President Bashar Assad, saying in a tweet on Sunday that Syria, Russia and Iran bear responsibility for the attack.

Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President Putin, Russia and Iran are responsible for backing Animal Assad. Big price... — Donald J. Trump (@realDonaldTrump) April 8, 2018

....to pay. Open area immediately for medical help and verification. Another humanitarian disaster for no reason whatsoever. SICK! — Donald J. Trump (@realDonaldTrump) April 8, 2018

The president told reporters that anybody involved, including Russian President Vladimir Putin, will "pay a price" for the attack, and promised a response to the attack within the next "24 to 48 hours."