France on Friday accused Bashar al-Assad and his allies of seeking to break Syria apart, as Russian-backed regime forces prepared to storm rebel-held eastern Aleppo.
Foreign Minister Jean-Marc Ayrault was also critical of Washington, accusing it of excluding its allies from the diplomatic search for a solution to the conflict.
"In bombarding Aleppo, the regime is playing the card of a partition of Syria, and his allies are letting him get away with it," he said, at the United Nations.
Ayrault said Assad's regime was trying to win sole control over the populous west of Syria, including Aleppo, Damascus and the Mediterranean coast.
"The situation can fairly be called desperate," he said.
On Thursday, on the sidelines of the UN General Assembly, Ayrault was one of more than 20 international ministers who met as the International Syria Support Group.
The ISSG, chaired by US Secretary of State John Kerry and Russia's Foreign Minister Sergei Lavrov, was set up to press for a ceasefire and a negotiated end to the war.
But Washington and Moscow have taken the lead in the process and this month negotiated a bilateral plan to impose a ceasefire, which promptly collapsed.
"The negotiations between the Russians and the Americans are continuing, but they seem interminable," Ayrault said, adding that the US has a "special responsibility."
"It's time to move to a more collective approach," he declared.
The ISSG meeting broke up with no new plan to salvage the ceasefire, but both US and Russian officials floated the possibility of more Kerry-Lavrov talks on Friday.