"We don't have any evidence right now that chemical weapons are being used," Manning said when asked to comment on the statement by Russian Foreign Minister Sergey Lavrov on Monday that Russia expects new disinformation campaigns regarding alleged use of chemical weapons in Syria to derail existing ceasefire agreements.
READ MORE: Terrorists Fire US-Made Weapons at Syrian Army in Eastern Ghouta
"We've seen the reports," Manning said. "We'll closely watch that, and condemn any use of chemical weapons on the Syrian people."
On Sunday, the Russian Defense Ministry said that militant group leaders in Syria are preparing provocations by using poisonous substances in the Eastern Ghouta enclave in order to accuse the Syrian government of using chemical weapons.
On Saturday, the UN Security Council unanimously adopted a resolution urging all parties to the conflict in Syria to immediately stop all clashes and adhere to a long-term humanitarian ceasefire on the entire territory of the country in order to ensure safe and unhindered delivery of humanitarian aid, as well as medical evacuation of those injured.
READ MORE: Terrorists in Syrian E Ghouta Hold 100s of Civilians Hostage — Russian Military
The Damascus suburb of Eastern Ghouta is one of the Syrian de-escalation zones that were created during the Astana talks on Syrian reconciliation, with Russia, Iran and Turkey serving as guarantors of de-escalation agreements.
The United Nations estimates that almost 400,000 people have been trapped in Eastern Ghouta besieged by government troops, while Russia argues that the Syrian capital has been attacked by militants controlling the enclave.