Russia's army on Saturday dismissed a French claim that Raqa, the Islamic State's stronghold in Syria, was surrounded by troops who were poised to storm it, saying it had "no relation to reality."
Russia's curt dismissal came a day after French Defence Minister Jean-Yves Le Drian said the jihadist group's de facto capital was "surrounded" and that the battle to prise it from IS control "will begin in the coming days."
"This will be a very hard battle but essential," he told France's CNEWS television, drawing a sceptical response from Russia.
"The optimism of the French defence minister, who said the encirclement of Raqa was complete... has no relation to reality or the situation on the ground," military spokesman Igor Konashenkov said in a statement.
"It is clear to any military specialist that the liberation of Raqa will not be a walk in the park for the international coalition," he said.
The duration of the operation and the measure of its success would depend on the ability of the players to "coordinate their action with all the forces fighting international terrorism in Syria," he said.
Konashenkov also drew a parallel with the US-backed ground offensive targeting Mosul, the jihadists' other stronghold in Iraq: "Even the most optimistic no longer believe Mosul will be completely liberated from IS this year."
The US-backed Kurdish-Arab alliance spearheading the fight in Syria, which has been working for months to encircle Raqa, also expressed caution about how soon the battle would begin.
Speaking to AFP on Friday, a spokesman for the Syrian Democratic Forces (SDF) said there was still work to do.
"The operation to besiege Raqa will take several weeks and that will then lead to the official launch of the operation," Talal Sello said.
And a European diplomat, who did not want to be named, said the situation surrounding the Raqa offensive remained "complex".
The anti-IS coalition estimates that between 3,000 and 4,000 jihadists are in Raqa, a city of about 300,000.