Russian President Vladimir Putin on Tuesday cancelled a long-planned trip to France amid diplomatic tensions between Paris and Moscow over the war in Syria.

"The president has decided to cancel this visit," a Kremlin spokesman told reporters.

"From the very start of his exchanges with his French colleague, President Putin noted that he is ready to visit Paris when it is comfortable for President Hollande. So we'll wait for when that comfortable time comes."

But French officials said their Russian counterparts had only discussed cancelling the trip, which was scheduled for next week, after they had proposed making it a "working visit" in which Putin and French President Francois Hollande held talks on Syria.

Hollande had told French media that he was considering ways in which he could use the trip to exert pressure on Russia over what he said was a "war crime" committed by Syrian pro-government forces with Russian support.

"Dialogue is necessary with Russia but it must be firm and frank," he said on Tuesday after the Kremlin's announcement.

The cancellation of the trip came after Russia vetoed a French proposal at the United Nations Security Council on Saturday calling on the Syrian government and its allies to halt the bombing of rebel-held areas of Aleppo.

France's draft called for an end to all military flights over Aleppo and to halt air strikes on the rebel-held east, which has 250,000 inhabitants.

On Monday, French Foreign Minister Jean-Marc Ayrault said French diplomats were working with prosecutors at the International Criminal Court to investigate alleged war crimes which France says are being committed by Syrian and Russian forces.

France is also looking into whether Russia can be targeted with new European Union sanctions over the conduct of its forces in Syria, where Moscow is President Bashar al-Assad's main military ally.

Putin had been due to open a new Russian Orthodox cathedral in the French capital.

Moscow appeared set to come under further diplomatic pressure from the UK on Tuesday with members of parliament set to hold an emergency debate on Syria, with Andrew Mitchell, a former cabinet minister and member of the governing Conservative Party calling the debate, on Monday accusing Russia of acting like Nazi Germany.

The Russian and Syrian air forces are widely accused of deliberately targeting hospitals and civilians in a renewed assault on eastern Aleppo, which has been besieged for weeks by pro-government forces.

According to the Syrian Observatory for Human Rights monitoring group, air strikes by the government and its Russian ally have claimed almost 300 lives, mostly civilians and including at least 53 children, since the 22 September launch of operations to reunite the government-held west and the east of Aleppo.

At least eight civilians were killed on Tuesday in the heaviest Russian bombardment in days of rebel-held areas of Syria's second city Aleppo, the Observatory said.

"This is the heaviest Russian bombardment since the Syrian regime announced it would reduce the bombardment" on 5 October, said Observatory head Rami Abdel Rahman.

An AFP correspondent in the city said that the victims of the latest attacks included two toddlers.

This article is available in French on Middle East Eye French edition.