A team of inspectors from the international chemical weapons watchdog is due to begin an investigation into a suspected chemical weapons attack near the Syrian capital Damascus.

It comes amid Western threats of retaliation and Russian warnings of the potential for “a dangerous escalation” in the area.

The fact-finding mission from the Organisation for the Prohibition of Chemical Weapons was expected to head to Douma, where the suspected attack took place and where Russia said rebels had now capitulated to government control.

The Syrian government said it would facilitate the mission’s investigation, which is to start on Saturday.

Syria and its ally, Russia, deny any such attack, which activists say killed more than 43 people last weekend.

Speaking at the United Nations on Thursday, Russia’s UN ambassador, Vassily Nebenzia, said the top priority had to be to avert a wider war, and he didn’t rule out the possibility of a US-Russia conflict.

Speaking to reporters after a closed emergency meeting of the UN Security Council, Mr Nebenzia said Russia was very concerned with “the dangerous escalation” of the situation and “aggressive policies” and preparations that some governments were 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,” Mr Nebenzia said, adding that “the danger of escalation is higher than simply Syria.”

The Security Council scheduled another emergency meeting for Friday morning at Russia’s request.

The imminent arrival of the chemical weapons inspectors came as rebels in Douma surrendered their weapons and left the town for opposition-held areas in the north.

Russia’s military said on Thursday that Douma was now under full control of the Syrian government after a Russian-mediated deal secured the evacuation of the rebels and thousands of civilians after it was recaptured by Syrian forces.

Douma and the sprawling eastern Ghouta region near the capital, Damascus, had been under rebel control since 2012 and was a thorn in the side of President Bashar Assad’s government, threatening his seat of power with missiles and potential advances for years.

The government’s capture of Douma, the last town held by the rebels in eastern Ghouta, marked a major victory for Assad.

Hamza Bayraqdar, spokesman for Jaysh al-Islam, the main rebel group that once controlled Douma, said his fighters had all evacuated. They handed over their heavy and medium weapons, as well as maps of land mines and the tunnels they dug, according to Syrian state media.

Douma and the rest of eastern Ghouta had been a significant rebel stronghold throughout Syria’s civil war and its surrender came after years of siege by Assad’s troops and a months-long military offensive.

It followed weeks of negotiations mediated by Russia that repeatedly were derailed.

A truce collapsed last week and the Syrian government pressed ahead with its military offensive.

Then came the suspected chemical attack in Douma, followed by international condemnation and threats of military action.

Amid conflicting tweets about the timing of any retaliation, US president Donald Trump said on Thursday that an attack on Syria could take place “very soon or not so soon at all.”

On Capitol Hill, US defence secretary Jim Mattis said the National Security Council would be meeting later on Thursday to present Mr Trump with various options, adding that he could not talk about any military plans because an attack “is not yet in the offing”.