The Pentagon Monday said it was “gravely concerned" by Russian reports that a new round of chemical attacks on Syria was imminent.

Defense Ministry Spokesman Maj. Gen. Igor Konashenkov told state-run media Sunday that a chlorine attack was expected in the next two days against Idlib province, and he predicted the attack would be executed by rebels themselves, executed from another rebel-held town about an hour south, Kafr Zita, in order to draw blame on the Syrian government.

play_circle_filled US strikes three Syrian sites in response for chemical attack The strikes were in retaliation for suspected chemical attacks by the Assad regime against a rebel-held Syrian town.

Kafr Zita was hit by chlorine in 2014 in an attack that was believed to be conducted by forces loyal to Syrian President Bashar Assad.

Pentagon spokesman Eric Pahon said Russia’s new statements left the Pentagon “gravely concerned.”

“We remain gravely concerned over open-source reports of a potential military offensive by the Syrian regime against civilians and civilian infrastructure in Idlib, which would result in devastating humanitarian consequences," Pahon said. “We also underline our concern at the potential for further — and illegal ― use of chemical weapons.”

Syrian children and adults receive treatment for a suspected chemical attack on Feb. 25, 2018, at a makeshift clinic on the rebel-held village of al-Shifuniyah in the eastern Ghouta region, on the outskirts of the capital Damascus. (Hamza Al-Ajweh/AFP via Getty Images)

Konashenkov said he based his prediction of an impending chemical strike on new U.S. military buildup in the Mediterranean ― similar to the U.S. buildup and military strike in April after Syria killed scores of civilians in a chemical attacks it launched on the rebel-held town of Douma. In the counter strike, air and sea forces from the U.S., U.K. and France launched 105 weapons onto three chemical weapons facilities operated by the Syrian government.

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Pahon, however, rejected the idea that the U.S. was again amassing forces in the Mediterranean.

“What I can tell you is that Russian reports of a U.S. military buildup in the eastern Med are nothing more than propaganda,” said spokesman Eric Pahon. “It’s not true. That does not mean, however, that we are unprepared to respond should the president direct such an action.”