Trump huddles with war cabinet, vows Syria decision 'fairly soon'

President Donald Trump gathered his top national security advisors on Thursday to weigh his military options in Syria, as Moscow warned against any move that risks triggering a conflict between Russia and the United States.

The drumbeat of military action appeared to grow louder as Russia stonewalled diplomatic efforts at the United Nations and France declared "proof" that Moscow's Syrian ally carried out a deadly chemical weapons attack that killed at least 40 Syrians on Saturday.

"It's too bad that the world puts us in a position like that," said Trump, as Defence Secretary James Mattis headed to the West Wing to present options for a retaliatory strike.

"We're having a number of meetings today, we'll see what happens, we're obviously looking at that very closely," he told lawmakers and governors in the Cabinet Room.

"Now we have to make some further decisions, so they will be made fairly soon," added first-term commander-in-chief, who earlier appeared to equivocate on the timing of strikes.

Meanwhile, Mattis told the House Armed Services Committee earlier on Thursday that, "some things are simply inexcusable, beyond the pale and in the worst interest of not just the chemical weapons convention but of civilization itself," reffering to the suspected chemical attacks. 

Read more: Can US respond to Syria chemical attack without risking escalation?

Since Saturday, when images of ashen toddlers struggling for breath emerged from Douma - the main city in the Eastern Ghouta enclave near Damascus that has been a crucible of revolt against Bashar al-Assad's regime - there has been a sustained military buildup in the eastern Mediterranean.

A French frigate, UK Royal Navy submarines laden with cruise missiles and the USS Donald Cook, an American destroyer equipped with Tomahawk land attack missiles have all moved into range of Syria's sun-bleached coast.

The Cook - named after a Marine Colonel who suffered depravation and starvation as a Vietnam prisoner of war - has past experience tangling with the Russian military, having been deployed to the Black Sea during the recent crisis in Crimea.

But half a world away in New York, Russia's UN ambassador warned the priority in Syria was to avert US-led strikes that could lead to a dangerous confrontation between the world's two preeminent nuclear powers.

"The immediate priority is to avert the danger of war," said Ambassador Vassily Nebenzia following closed-door Security Council talks.

Asked if he was referring to war between the US and Russia, he said: "We cannot exclude any possibilities unfortunately."

Read more: Is the Syrian war about to get even more complicated?

Trump has slammed Russia for its partnership with "gas killing animal" Assad, spurring concerns that a US strike could lead to a conflagration with Russia, which has major military facilities at Tartus and Hmeimim and works cheek-by-jowl with Syria forces that could be targeted.

US officials have refused to rule out direct military engagement with Russia, with the White House saying "all options are on the table."

But a special hotline for the US and Russian militaries to communicate about operations in Syria is active and being used by both sides, Moscow said on Thursday.

Chemical disarmament once and for all?

At the United Nations meanwhile, diplomats were mulling a draft resolution put forward by Sweden and obtained by AFP, that would dispatch a "high-level disarmament mission" to rid the country of chemical weapons "once and for all."

But that may prove too little, too late. 

The UN Security Council, tasked with maintaining international peace and security has been riven, with Moscow virulently denying the Douma attack took place, or postulating that it was carried out by rebels.

The council has already failed to agree on a response to the attack in three votes and has been deadlocked throughout the Syrian civil war.

In Paris, France's Emmanuel Macron upped the pressure on Moscow by stating he had "proof" that the Assad's regime had used chemical weapons, and vowing a response "at a time of our choosing."

In London, British Prime Minister Theresa May held an emergency cabinet meeting to discuss support for US action against the Syrian regime.

After the meeting, the British leader reiterated there was a "need to take action" in Syria, and that the government would "continue to work with allies in the United States and France to coordinate an international response".

But across Western capitals opposition to military action also grew. US lawmakers questioned whether Trump has the legal authority to order strikes without Congressional approval and opposition parties voiced concern.

National security experts worried about whether strikes would actually serve to deter Assad. 

Read more: Comment : Trump's phoney war against Assad

In April last year Trump ordered Tomahawk strikes on the Shayrat Airbase in response to a similar chemical weapons attack on rebel-held Khan Sheikhoun.

But the pinpoint strike did not deter Assad, and US officials, speaking on condition of anonymity, have since investigated as many as 10 suspected chemical attacks.

The same officials say Syria has continued to produce or procure chlorine, which also has industrial and agricultural uses.

Syria, which denies carrying out the latest attack, said it had invited the Organisation for the Prohibition of Chemical Weapons (OPCW), which has blamed the regime for previous such incidents, to visit Douma.

The OPCW, which works to rid the world of chemical arms stockpiles, said its experts were on their way to Syria and will start their work on Saturday.