Russia has warned of the possibility of war with the United States if the US and its European allies go through with the threat of military strikes in Syria.

US President Donald Trump said Friday morning he is holding meetings on Syria in response to a suspected poison gas attack and expects decisions to be taken “fairly soon.”

Fears of confrontation between Russia, Syria’s big ally, and the West have been running high since Mr Trump said on Wednesday that missiles “will be coming” after the attack in the Syrian town of Douma on April 7, and criticised Moscow for standing by Syrian President Bashar al-Assad.

The President appeared to attempt to cool the situation Thursday night when he tweeted: “Never said when an attack on Syria would take place. Could be very soon or not so soon at all!” 

But he later added: “We’re having a number of meetings today, we’ll see what happens. Now we have to make some … decisions, so they’ll be made fairly soon.”

The British Cabinet has given Prime Minister Theresa May the go ahead to join the US and France in planning military strikes in response to the alleged Syrian chemical weapons attack.

After meeting for more than two hours, the Cabinet on Friday morning backed Ms May’s plan to work with the two allies “to coordinate an international response.” But it gave no indication of the timing or scale of any action.

Russia’s ambassador to the United Nations, Vassily Nebenzia, later said the top priority was to avert war in Syria and refused to rule out the possibility of a US-Russian conflict.

Mr Nebenzia said Russia is very concerned with “the dangerous escalation” of the situation and “aggressive policies” and preparations that some governments are making, a clear reference to the Trump administration and its allies.

“We hope that there will be no point of no return — that the US and their allies will refrain from military action against a sovereign state,” he said.

Mr Nebenzia told reporters after a closed emergency meeting of the UN Security Council that “the danger of escalation is higher than simply Syria, because our military are there on the invitation of the Syrian government”.

French President Emmanuel Macron earlier said France will decide whether to strike back when all the necessary information has been gathered.

“We have proof that last week … chemical weapons were used, at least with chlorine, and that they were used by the regime of (President) Bashar al-Assad,” Mr Macron said.

Syria and its backers, Russia and Iran, say reports of the attack were fabricated and have accused the US of using it as a pretext to attack the government.

But a team of experts from the global chemical weapons watchdog, the Organisation for the Prohibition of Chemical Weapons, was travelling to Syria and will start their investigations on Saturday, it said.

Despite the tension, there were signs of a global effort to head off a direct confrontation between Russia and the West.

The Kremlin said a crisis communications link with Washington, created to avoid an accidental clash over Syria, was in use.

There was no direct word from Russian President Vladimir Putin, although he discussed the situation with Turkish President Tayyip Erdogan by phone, the Interfax news agency said.

Syria’s military has repositioned air assets alongside the Russian military hoping Washington will be more reluctant to hit them.

Ms May has ordered British submarines to move within missile range of Syria in readiness for strikes against the Syrian military that could begin as early as Thursday night, London’s Daily Telegraph newspaper said on Wednesday.

Chancellor Angela Merkel says Germany won’t participate in possible military action in Syria, but supports sending a message that the use of chemical weapons is unacceptable.

-with AAP