Russia and the US, the world's two most powerful militaries and biggest nuclear powers, appear set to clash over a suspected chemical weapons attack in Syria.

President Donald Trump told Russia to "get ready" for US missiles, and he is reportedly weighing a much bigger strike on Syria than the one last April, which did little long-term damage.

A Russian official threatened shooting down incoming US missiles and also targeting the platforms used to launch them, which could mean sinking US Navy ships.

The US and Russia, the world's two most powerful militaries and biggest nuclear powers, appear set to clash over a suspected chemical weapons attack in Syria, with President Donald Trump tweeting Wednesday for Russia to "get ready" for a US missile strike.

"Russia vows to shoot down any and all missiles fired at Syria," Trump tweeted. "Get ready Russia, because they will be coming, nice and new and 'smart!' You shouldn’t be partners with a Gas Killing Animal who kills his people and enjoys it!"

The first part of the tweet referred to comments by a Russian diplomat threatening a counterresponse to any US military action against the Syrian government, which the US and local aid groups have accused of carrying out several chemical weapons attacks on its own people.

According to Reuters, Russia's ambassador to Lebanon, Alexander Zasypkin, told the militant group Hezbollah's Al-Manar TV that, "If there is a strike by the Americans," then "the missiles will be downed and even the sources from which the missiles were fired."

Trump canceled a trip to South America over the latest suspected chemical attack, which killed dozens on Saturday, and is instead consulting with John Bolton, his new ultra-hawkish national security adviser. Trump and France have promised a strong joint response in the coming days.

The president and his inner circle are reportedly considering a much larger strike on Syria than the one that took place almost exactly a year ago, on April 7, 2017, in which 59 US sea-based cruise missiles briefly disabled an air base suspected of playing a role in a chemical attack.

This time Trump has French President Emmanuel Macron in his corner — but also acute threats of escalation from Syria's most powerful ally, Russia.

"The threats you are proffering that you're stating vis-à-vis Syria should make us seriously worried, all of us, because we could find ourselves on the threshold of some very sad and serious events," Russia's ambassador to the United Nations, Vassily Nebenzia, warned his US counterpart, Nikki Haley, in a heated clash at the UN.

The US wants a massive strike, but Russia won't make it easy

The Russian S-400 "Triumf," also known by its NATO code name of SA-21 "Growler," produced by the Almaz-Antey Central Design Bureau. NOSINT

Syrian government forces present a more difficult target than most recent US foes. Unlike Islamic State fighters or Taliban militants, the Syrian government is backed by heavy Russian air defenses. Experts on these defenses have told Business Insider the US would struggle to overcome them, even with its arsenal of stealth jets.

It was US Navy ships that fired the missiles in the April 7, 2017, strike. If Russia were to retaliate against a US Navy ship with its own heavy navy presence in the region, the escalation would most likely resemble war between the two countries.

Vladimir Shamanov, a retired general who heads the defense affairs committee in Russia's lower house of parliament, would not rule out the use of nuclear weapons in an escalation with the US over Syria, saying only that it was "unlikely," the Associated Press reports.

The US has destroyer ships in the region, The New York Times reports, as well as heavy airpower at military bases around the region. While Russian air defenses seem credible on paper, they seem to have done nothing to stop repeated Israeli airstrikes all around Syria.

US's and Russia's military reputations on the line

A US Air Force F-22 Raptor flying over the Arabian Sea in support of Operation Inherent Resolve in 2016. US Air Force photo by Staff Sgt. Corey Hook

On both the Western and Russian sides of the conflict, credibility is on the line. The leaders of the US and France have explicitly warned against the use of chemical weapons, saying they will respond with force. Russia has acted as a guarantor of Syrian President Bashar Assad's safety in the face of possible Western intervention but has found itself undermined by several strikes from the US and Israel.

Experts previously told Business Insider that an outright war with the US would call Russian President Vladimir Putin's bluff and betray his true aim of projecting power at low cost, while destroying much of his military.

Additionally, the Syria government, backed by Russia, has struggled to beat lightly armed rebels who have lived under almost nonstop siege for the past seven years.

For the US and France, failure to meaningfully intervene in the conflict would expose them as powerless against Russia and unable to abate the suffering in Syria even with strong political will.

For now, the world has gone eerily quiet in anticipation of fighting.

European markets dipped slightly Wednesday on expectations of military action, and the skies around Syria have gone calm as the pan-European air-traffic control agency Eurocontrol warned airlines about flying in the eastern Mediterranean because of the possibility of an air war in Syria within the next 48 hours.