Russian Foreign Minister Sergey Lavrov says the information the U.S. showed Moscow trying to prove that the Syrian regime was behind an alleged chemical weapons attack is "absolutely unconvincing."

Lavrov said Monday "there was nothing specific" in the evidence presented by Washington: "no geographic coordinates, no names, no proof that the tests were carried out by the professionals." He did not say what tests he was referring to.

The United States insists Syrian President Bashar Assad's troops were behind the chemical attack on Aug. 21, which they say killed over 1,400 people, and is considering strikes against his regime. Moscow is Assad's key ally and weapons supplier, and its protector at the United Nations.

Lavrov say U.S. officials said they cannot share with them all the evidence because some of it is classified.