Sidelined from the US-Russia negotiations on chemical weapons, France is determined that demands for President Bashar al-Assad to be tried for war crimes do not drop off the rapidly shifting international agenda.

Publicly, France hailed Saturday's deal in Geneva to eliminate Assad's deadly chemical arsenal by mid-2014.

But privately there is disquiet in Paris about an accord that some fear could bestow renewed legitimacy on Assad, consolidate his grip on power and stall moves to bolster the opposition coalition that France has championed.

Diplomats say that was reflected in the double-edged statement issued by Foreign Minister Laurent Fabius in response to the Geneva deal.

While praising it as a "significant step forward", Fabius also emphasised that the next steps should be shaped by the contents of a report, due to be published Monday, by UN inspectors probing the August 21 chemical weapons attack outside Damascus.

France's Socialist government unequivocally backed punitive military action in response to what they regard as a watershed moment in Syria's civil war, and Fabius has indicated that he expects the UN report to point a finger of blame in the direction of the regime.

"What we are saying is that the Geneva accord does not settle all accounts," said a well-placed French official. "It is not a stamp of approval for Assad, whom we simply do not trust. There is a lot more involved."

After a whirlwind visit to China on Sunday, Fabius is due to hold talks with his British counterpart William Hague and US Secretary of State John Kerry in Paris on Monday before flying to Moscow on Tuesday.

French President Francois Hollande will also have a brief meeting with Hague, Kerry and Fabius on Monday.

The diplomatic flurry, officials say, reflects a determination in the French government to defend their bottom lines: no impunity for Assad and his cronies, whom they want hauled before the International Criminal Court, and no let-up in the search for a political solution to a conflict that has left more than 110,000 people dead and more than a million displaced or refugees.

To date, the French vision of how a political solution could be achieved has centred on steadily increasing support for the rebels with a view to tilting the military balance within Syria in their favour.

That approach was reflected in Paris effectively recognising the opposition as a government in exile and in a campaign to relax a European embargo on arms transfers to Syria.

-- 'France cannot act militarily on its own' --

But enthusiasm for arming the rebels has waned as it has become increasingly clear that hardened Islamist radicals are a significant force within the coalition, triggering memories of how Western funds allowed Osama bin Laden to develop Al-Qaeda in Afghanistan in the 1980s.

Camille Grand, an analyst with the French Foundation for Strategic Research (FRS), says France's hawkish stance on Syria has been consistent in terms of principles and coherent in terms of how a solution can practically be achieved.

But he said Fabius had had the rug pulled from under him by first Britain's and then the United States' retreat from the threat of strikes against Assad.

"These are the realities. France cannot act militarily on its own and has had to adjust its positions in reaction to the shifts of its two natural allies."

Caught off balance by Russia's chemical weapons initiative, France's focus in the coming days and weeks will be securing the toughest possible terms for the UN resolution that will put the Geneva accord into force.

France has already circulated a draft that would authorise military action in the event of non-compliance by Assad but there has been no sign yet that Russia would be prepared to sign up to terms it described as unacceptable last week.

In Geneva on Saturday the issue was fudged, with the Russians saying they could accept provision for some unspecified sanctions if Assad fails to do what he has promised and the United States saying the issue of a resort to force would be discussed if and when it becomes relevant.

While it has become increasingly apparent that France and the United States are no longer on the same page on Syria, French officials say their determination to stick to a firm line has helped deliver the progress achieved in Geneva.

"We would not be where we are today if we had not set the bar as high as we did, if we hadn't been as demanding," one said.

Speaking on condition of anonymity, the official acknowledged that the UN report due out Monday would be pivotal. "It will be much easier for us to obtain the support of a maximum number of Security Council members for a strong resolution if the report is severe," he said.

UN Secretary General Ban Ki-Moon has said the report will provide overwhelming evidence that a chemical weapons attack occurred and, in an indication that he holds the regime responsible, has accused Assad of committing multiple war crimes.

["Francois Hollande gives a press conference at the Elysee Palace in Paris on Wednesday" via AFP]