French Foreign Minister Jean-Marc Ayrault on Sunday blamed Syrian President Bashar al-Assad's regime for undermining the ceasefire deal brokered by Russia and the United States, and said the agreement must be salvaged "at all costs."

"We must not forget that it is first of all the (Syrian) regime, and it is always the regime, which has jeopardized the US-Russian ceasefire," said Ayrault in New York.

The faltering US-Russian deal for Syria is set to dominate the agenda as world leaders gather at the United Nations this week for the annual General Assembly meeting.

"If there is one thing that must emerge from this General Assembly meeting it is hope for peace" in Syria, Ayrault said on the sidelines of a ceremony held to commemorate the September 11 attacks.

World leaders "must latch on to this agreement and keep it alive at all costs", he said.

After months of negotiations, the United States and Russia reached the agreement on September 9 that calls for a ceasefire, the delivery of aid and the joint targeting of Islamist rebels in Syria.

A ceasefire that had been in force for nearly a week was on the brink of collapse on Sunday when rebel-held districts of Aleppo came under a barrage of air strikes.

Russia, Syria's main ally, accused the United States of endangering the deal after a US-led coalition strike that killed dozens of Syrian soldiers in the east, near the Islamic State-controlled town of Deir Ezzor.

A UN Security Council meeting held late Saturday saw the US and Russian envoys trading barbs following the airstrike, for which the United States has expressed regret.

US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov are due on Wednesday to attend a special Security Council meeting on Syria.