The arrival in Damascus of a chemical disarmament team on Tuesday is the result of an unprecedented, gruelling US-Russian deal that averted regional war.

When a Syrian government delegation arrived in Moscow on September 9, its members did not know that Russian President Vladimir Putin would take a decision hours later that would change the course of history.

Syria's Foreign Minister Walid Muallem, his deputy Faisal Muqdad and presidential adviser Buthaina Shaaban arrived in Moscow at their Russian backers' request.

Led by the United States, the West was threatening a military intervention in Syria after a deadly sarin attack killed hundreds near Damascus on August 21.

While Washington was convinced President Bashar al-Assad's regime was responsible for the attack, Moscow blamed the rebels.

Muallem met with his Russian counterpart Sergei Lavrov and asked what had happened when Putin and US President Barack Obama had met on the sidelines of the G-20 meeting in Saint Petersburg on September 6.

Lavrov said he had not yet been briefed by the Kremlin.

The surprise came hours later, when Lavrov told his guests that "Russia intends to make a proposal that would put Syria's chemical arsenal under international supervision and that it be destroyed," said a diplomat close to the issue.

Lavrov then advised the Syrian delegation to comply with this decision, and gave them three hours to make up their minds, the diplomat added.

He told them Putin had come away from his meeting with Obama convinced the United States was ready to strike Syria.

"It would have been catastrophic because the strike would have destroyed the whole of Syria's military infrastructure, and would have allowed the rebels to enter into Damascus," the diplomat said.

"That would have meant the fall of the regime, a scenario that had to be avoided at any cost."

But some members of the Syrian delegation expressed concerns to Lavrov over the proposed deal, a participant in the meeting said.

"The point of these chemical arms was to maintain the strategic balance with Israel, which has nuclear weapons, and this decision makes us more fragile," a member of the Syrian delegation told the Russian foreign minister.

"Your best weapon is us," Lavrov responded firmly.

The Syrian delegation contacted Assad in Damascus, who gave his consent to the chemical weapons deal.

Lavrov then announced that he had asked his Syrian guests to turn the country's chemical arsenal over to international control.

The origins of the chemical weapons deal were in an idea first expressed by US Secretary of State John Kerry.

Asked in London what Assad could do to avoid a US strike, Kerry said: "He could turn over every single bit of his chemical weapons to the international community in the next week.

"Turn it over, all of it, without delay, and allow a full and total accounting for that."

But he quickly seemed to shoot down his own idea, adding: "But he isn't about to do it, and it can't be done, obviously."

State Department spokeswoman Jen Psaki issued an email saying Kerry "was making a rhetorical argument about the impossibility and unlikelihood of Assad turning over chemical weapons he has denied he used".

But Kerry's statement had caught the Russians' attention.

While on the plane back to Washington, Kerry received a phone call from Lavrov, in which he said Russia accepted his proposal.

A deal for everybody

"All hell broke loose on the plane as no one knew what was going on," said a journalist who was on the plane.

The White House also accepted the idea quickly.

Kerry and Lavrov met again in Geneva, where on September 14 they struck a deal that gave Damascus a week to hand over a list of its chemical arms stockpiles.

They also agreed the arsenal would be destroyed by mid-2014.

The deal suited nearly all sides involved in the conflict.

"It's been a year since the United States has been negotiating with Moscow, to try to convince Russia to (ensure) Syria's chemical weapons are handed over," said Andrei Baklitkyi, an expert at the Moscow PIR-Tsentr political studies centre.

Obama was also having trouble convincing US Congress of the need for a strike.

And Russia came out a winner because its Mediterranean fleet would have looked feeble if it had failed to respond to a strike on its ally Syria.

For Assad, the deal was crucial for his regime's survival.

"It's a good deal, because everyone has gained from it," said a Syrian official.

The only loser, perhaps, is the Syrian opposition, much of which had backed US military action, believing it would mean the swift fall of Assad's regime.