White nationalist leader Richard Spencer of the National Policy Institute Reuters/Spencer Selvidge

Key members of the white nationalist alt-right movement have abandoned their support for Donald Trump after he authorised missile attacks against Syria.

Members of the movement have for years lauded Trump as a bulwark of their nationalist agenda, praising the outspoken tycoon for his criticism of the liberal world order and Nato.

However many have taken to Twitter to express their dismay, after the US launched missile attacks on a Syrian air base from where planes on Tuesday set off to launch chemical attacks on the town of Khan Sheikhoun.

Alt-right blogger and conspiracy theorist Paul Joseph Watson tweeted "I'm officially OFF the Trump train" in the wake of the attacks in the early hours of Friday. Watson had played a key role in spreading fake news dedicated to undermining Trump's rival, Hillary Clinton during the US presidential election campaign.

"Syria was no threat to America," tweeted US blogger John Paul Ramsay, who has been accused of spreading anti-Semitic hate speech, and implied Israel was behind Trump's decision, branding Trump "Israel's b***h".

Alt-right ideologue Richard Spencer called the strike "a sad, shocking and deeply frustrating moment."

"I condemn the strikes," he said. "I'm going to wait and see. Perhaps Trump is slapping Assad across the nose and won't go further. Perhaps Russia was informed of the attacks. Worst case scenario: We're replaying the 2000s: A conservative comes to office on a populist message and becomes a globalist and neocon shill. Again I'll wait and see but I'm prepared to denounce Trump."

The alt-right is the term given to a loose assortment of anti-establishment conservatives and white nationalists who formed the vanguard of Trump's online support during the presidential election.

Just days after Donald Trump Jr suggested he be given a Pulitzer Prize, blogger Mike Cernovich hosted a marathon Periscope livestream, in which he voiced the views that Assad had been framed for the chemical attack, and that Trump was being manipulated by the "deep state."

In addition to supporting Trump's 'America first' isolationist policies and anti-interventionist rhetoric many members of the alt-right have shown a marked fondness for Syria's chief international ally, Russia.

Members of the movement have suggested that Trump ought to provide support to Assad in the battle against Islamist militants.