The US State Department says it is "confident" the Syrian Government was responsible for a suspected chemical weapons attack in the rebel-held Syrian town of Douma one week ago.

Key points: The emergency meeting is scheduled for Friday evening

The emergency meeting is scheduled for Friday evening Inspectors will begin an investigation of the alleged chemical attack site in Douma

Inspectors will begin an investigation of the alleged chemical attack site in Douma Lebanon's Hezbollah says there's no risk of a US-Russia war

But Russia's Defence Ministry claimed Britain was involved in "faking" the attack, which a Syrian medical relief group said killed at least 60 people, including children.

"We can say that the Syrian Government was behind this attack. We know that this was a chemical weapon that was used. The exact kind or the mix, that we are still looking into. A lot of this stuff is classified at this point," State Department spokeswoman Heather Nauert said.

White House press secretary Sarah Huckabee Sanders said United States officials at various levels were still consulting with allies about possible retaliatory military strikes.

"We also hold Russia responsible for their failure to stop chemical weapons attacks from taking place," Ms Sanders said.

US President Donald Trump threatened missile strikes on Syria in a tweet on Wednesday, warning Syria's main ally Russia to "get ready".

Two days later the US is yet to act.

Sorry, this video has expired US and Russia clash at UN over Syrian chemical strike

US ambassador to the United Nations Nikki Haley said Mr Trump was not letting anyone rush him into a decision on possible military action against Syria.

"You don't rush decisions like this," Ms Haley said.

"If you rush decisions like this you make a mistake.

"What we're making sure is that we have all the information to know if we do something what will happen, how will it happen and will it hurt anyone."

US media reported that Defence Secretary James Mattis had so far dissuaded the President from ordering strikes against Syrian targets, fearing that to do so would spark a dangerous confrontation with Russia and Syria's ally Iran.

Earlier this month Mr Trump reportedly told Pentagon officials that he wanted to end the US involvement in Syria.

Kremlin's fake claim a 'grotesque lie'

In a televised briefing on Friday, Russia's Ministry of Defence repeated the Kremlin's stance that the attack was faked, adding that it had proof that Britain participated in its staging.

"We have … evidence that proves Britain was directly involved in organising this provocation," defence ministry spokesman Igor Konashenkov said.

Mr Konashenkov said that Russia knew "for sure" that between April 3 and April 6, the White Helmets — a group which helps civilians in opposition-held territory in Syria — were "under severe pressure specifically from London to produce as quickly as possible this pre-planned provocation".

Britain's UN Ambassador Karen Pierce denied Britain was in any way involved.

"This is grotesque, it is a blatant lie, it is the worst piece of fake news we've yet seen from the Russian propaganda machine," Ms Pierce told reporters.

Russia's Foreign Minister Sergey Lavrov earlier voiced the theory that the attack was staged.

"Intelligence agencies of a state that is now striving to spearhead a Russophobic campaign were involved in that fabrication," he said.

Moscow, he said, has "irrefutable information that it was another fabrication".

Mr Lavrov did not offer evidence to back up his claim.

Speaking to reporters in Moscow, he reiterated warnings to the West against military action saying that even the smallest miscalculation in Syria could lead to new waves of migrants and that ultimatums and threats did not help the dialogue.

"God forbid anything adventurous will be done in Syria following the Libyan and Iraqi experience," Mr Lavrov told a news conference on Friday.

A medical worker giving toddlers oxygen through respirators following the alleged poison gas attack. ( Syrian Civil Defense White Helmets via AP )

'The Cold War is back'

UN Secretary-General Antonio Guterres has warned the Middle East is in such "chaos" that it has become a threat to international peace and security — and Syria "represents the most serious threat".

The UN chief told an emergency meeting of the UN Security Council on Friday that the highly volatile situation in the region risks "escalation, fragmentation and division as far as the eye can see, with profound regional and global ramifications".

"The Cold War is back — with a vengeance but with a difference," Mr Gutteres said.

"The mechanisms and the safeguards to manage the risks of escalation that existed in the past no longer seem to be present."

The UN Security Council scheduled Friday's emergency meeting after Russia's UN ambassador Vassily Nebenzia raised concerns over the "the dangerous escalation" of the situation in Syria.

Mr Nebenzia said Russia was very concerned with "the dangerous escalation" of the situation and "aggressive policies" and preparations that some governments were making.

Russian Deputy Prime Minister Arkady Dvorkovich said on Friday international relations should not depend "on the mood of someone on the other side of the ocean when he wakes up", in apparent reference to Mr Trump.

Fears of confrontation between Russia, the Syrian state's key ally, and the West ran high after Mr Trump said missiles "will be coming" and lambasted Moscow for standing by Syrian President Bashar al-Assad.

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Mr Trump has since tempered his remarks on attacking Syria and even as he consulted allies Britain and France, there were signs of efforts to prevent the crisis from spiralling out of control.

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The White House said "no final decision has been made" on Syria after Mr Trump met his national security team.

'Immediate priority to avert the danger of war'

Mr Nebenzia told reporters after a closed council meeting on chemical weapons in Syria that Russia was calling for the emergency meeting to hear from UN Secretary-General Antonio Guterres on the threat to international peace and security from possible military action against Syria.

"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," Mr Nebenzia said.

He said it was a priority to get inspectors from the Organization for the Prohibition of Chemical Weapons (OPCW) to the Damascus suburb of Douma, where the suspected gas attack took place last weekend, so they could see what happened — and "that nothing prevents them from doing it".

The OPCW said the investigators would start work on Saturday (local time).

"The immediate priority is to avert the danger of war," Mr Nebenzia said.

Hezbollah deputy leader Sheikh Naim Qassem downplayed the rising tensions in Syria saying he did not believe it would spiral into a direct US-Russia conflict or a wider all-out war.

The heavily armed Shiite Hezbollah movement has been a vital military ally of Mr Assad in the seven-year war.

"We rule out the situation developing into a direct American-Russian clash or a wide state of war," Sheikh Naim Qassem told Lebanese daily al-Joumhouria in an interview.

"The conditions do not point to a total war happening ... unless Trump and [Israeli Prime Minister Benjamin] Netanyahu completely lose their minds," he said.

Russia's military said Douma had been brought under full control of the Syrian government under a Russia-mediated deal that secured the evacuation of the rebels and thousands of civilians after it was recaptured by Syrian forces.

The Government, however, said evacuations from Douma were ongoing and no Syrian Government forces had entered the town.

Mr Lavrov noted that Russian and US militaries had a hotline to prevent incidents, adding that it was not clear if it would be sufficient amid mounting tensions.

Children receive medical treatment after the alleged poison gas attack in Douma. ( AP: Syrian Civil Defence White Helmets )

AP/Reuters