"What the US administration describes as irrefutable evidence... is nothing but tired legends that the terrorists have been circulating for more than a week, with their share of lies and entirely fabricated stories," a foreign ministry statement read out on state television said.

A US intelligence report released on Friday concluded the regime had launched a chemical onslaught in the suburbs of Damascus last week, killing 1,429 people, including at least 426 children.

US Secretary of State John Kerry said that the report gathered evidence from thousands of sources and that the intelligence community has "high confidence" that the regime was responsible for the attack.

But in its statement, the Syrian foreign ministry dismissed the report as a poorly crafted document informed mostly by social media.

It expressed surprise that "a superpower could mislead its opinion so clumsily, relying on evidence that does not exist, and that the United States could base policies on matters of war and peace on social media and websites."