 -- As Syrian president Bashar al-Assad called videos of last week’s chemical attack a “fabrication,” a piece of propaganda promoted by a Russian cyber operation and bearing the hashtag #SyriaHoax has gained traction in the United States, analysts tell ABC News.

Following the chemical weapons attack that killed dozens of civilians on Tuesday, Al-Masdar News, a pro-Assad website based in Beirut, published claims that "something is not adding up in [the] Idlib chemical weapons attack." Its author cited "holes" in the accounts provided by the "Al-Qaeda affiliated" White Helmets leading to the conclusion that "this is another false chemical attack allegation made against the government."

That hoax story was promoted by a network of Russian social media accounts and ultimately picked up by popular alt-right personalities in the United States, including Mike Cernovich, one of the leading voices in the debunked 'Pizzagate' conspiracy theory. Cernovich popularized its new hashtag -- #SyriaHoax -- and sent it soaring through cyberspace. According to Trends24, within hours of the retaliatory missile strike President Donald Trump launched on Thursday night, #SyriaHoax was the No. 1 trending Twitter topic in the United States.

J.M. Berger of The International Centre for Counter-Terrorism at The Hague, who studies propaganda and social media analytical techniques, said #SyriaHoax is "a clear example of a Russian influence campaign" designed to undermine the credibility of the U.S. government.

"The point of an influence campaign is to get people involved who wouldn't otherwise be involved," Berger said. "A lot of people in the alt-right would not necessarily characterize themselves as being pro-Russian, but they're receiving influence from this campaign."

Berger cannot say whether Al-Masdar News is backed by either the Syrian government or the Russian government, only that the outlet "is being promoted at an extraordinary level by this [Russian] network" and the Kremlin has a history of weaponizing disinformation.

"This is a new iteration of an old type of warfare," Berger said. "We saw the Soviet Union use tactics like this during the Cold War. The difference is that you can do it on an industrial scale at a very low cost without deploying actual operatives on the ground of a foreign country."

This latest social media coup comes just months after Russia's attempts to use similar tactics to meddle with the U.S. presidential election, which U.S. officials believe was undertaken by a secretive Russian intelligence operation based in St. Petersberg tasked with manipulating public opinion.

Senator Mark Warner, the ranking Democrat on the Senate Intelligence Committee investigating those efforts, says a close examination of the evidence so far reveals a disturbing timeline running throughout the campaign. WikiLeak's release of Hillary Clinton campaign chairman John Podesta's Russian-hacked emails -- just 29 minutes after The Washington Post published an explosive video showing Donald Trump making sexually explicit comments during an Access Hollywood shoot -- raised particular concerns.

"That was more than coincidence," Warner said. "It is so outrageous that a foreign nation came in and manipulated our news, hacked into personal information leaked it out on a selective basis."

According to Ciaran Martin, the head of a newly created national cybersecurity operation at Britain's GCHQ, which provided U.S. officials with the first indication that the Russians had hacked the Democratic Party, activity like this hasn't slowed down since the presidential election in November. It's actually on the rise.

"I think we’ve seen a significant increase in Russian aggression in cyberspace over the past two years," Martin said. "We see attacks from state actors on a very frequent basis ... It has not plateaued. It is continuing to increase."

John Carlin, the former assistant attorney general for national security and an ABC News consultant, said the U.S. has less than four years to find a way to protect its election process.

"They’re going to come after us again in 2020," Carlin said. "If anything it may be more severe ... They’re probably going to come back with more skill, more desire to cause impact, and between now and then, we need to make sure they don’t succeed."

ABC News' Rhonda Schwartz, Cho Park and Matthew Mosk contributed to this report.