Douma, on the outskirts of Damascus, was the last rebel-held area in the eastern Ghouta region.
The remarks came a day after US President Donald Trump warned Russian Federation that his country would launch missile attacks on Syria after the alleged chemical attack took place. "I just want to remind you one more time it's 2018, it's not the middle of the 20th century", she said, adding that in a time of instant communications there's no reason "why people who are in charge of our security and worldwide peace can't talk". Russian Foreign Ministry Spokeswoman Maria Zakharova cannot even imagine that either Russian or American blood could be spilt in Syria, she said in an interview with Sky News on Thursday. On Wednesday he went even further, warning Russian Federation "to get ready" after Moscow vowed to shoot down any missiles fired at Syria.
The Russian military insists that the Douma attack might have been staged, adding that its units, dispatched to the site, found no traces of chemical weapons.
Mr. Mattis' remarks at a House Armed Services Committee hearing followed a series of Trump tweets this week that initially indicated he was committed to bombing Syria but later suggested he was awaiting further advice and assessment. "When I leave here, I go to a meeting where the National Security Council will be meeting on this and we will take forward various options to the president".
Syrian President Bashar al-Assad has warned the Western states against any military action on his homeland. France has also said it would join the military action.
"And announcing military actions over Twitter is the height of irresponsibility and contradicts the President's own previous commitment never to disclose America's plans publicly", Markey said.
Mr. Mattis said that although the United States has no hard proof, he believes the Syrian government was responsible for Saturday's attack.
The Kremlin was speaking as British ministers planned to gather to discuss whether to join the United States and France in a possible military attack on Syria that threatens to bring Western and Russian forces into direct confrontation. In a statement, Senator Bernie Sanders said Trump has no legal authority for broadening the war in Syria. Russian President Vladimir Putin called for the creation of a broad global coalition against terrorism during his speech at the United Nations back in 2015, Zakharova reminded, adding that the proposal "is still on the table".
The OPCW, which works to rid the world of chemical arms stockpiles, said its experts were on their way to Syria and will start their work on Saturday.