The U.S. State Department said Friday that it has proof that Syria was behind the suspected gas attack that left more than 40 civilians dead in Douma last week. Heather Nauert, a department spokesperson, said officials are still trying to determine what kind of chemical was used in the attack.

She said there was a "very high-level of confidence" that Syria was behind the attack, but did not elaborate on what type of evidence the department has.

"We believe we know who was responsible for this. We will still wait -- the Organisation for the Prohibition of Chemical Weapons (OPCW) will still formulate its facts and its findings, but it does not determine the responsibility, they determine the substance," Nauert said Friday.

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Nauert also refuted Russia's claim that the alleged gas attack had been staged by the U.K., calling the accusation "one of a long list of instances in which Russia takes information and they try to turn it upside down."

"We've seen a long history of the Russian government sow discord, whether it's in our own election process or other countries," she said. "They try to change the story but the facts are exactly what they are. Russia has changed its story once again because the facts have become too inconvenient for them."

President Trump on Thursday discussed U.S. military options to respond to the alleged chemical attack with his advisors and American allies, but has not made a final decision on his response.

Mr. Trump and British Prime Minister Theresa May agreed Syrian President Bashar al-Assad's alleged use of chemical weapons should not go unchallenged. Britain, the U.S. and France are working together on an international response, CBS News national security correspondent David Martin reports.