“These are acts that beg for an appropriate investigation of war crimes,” Kerry said. “They’re beyond the accidental now, way beyond, years beyond the accidental. This is a targeted strategy to terrorise civilians and to kill anybody and everybody who is in the way of their military objectives.”

The US has little chance of being able to initiate a war crimes probe of either Russia or Syria. Russia has veto power at the UN Security Council and has blocked repeated attempts over the last 5½ years to put pressure on Syrian President Bashar Assad’s government or hold it accountable for the widespread allegations of indiscriminate killing, torture and chemical weapons attacks.

Ayrault spoke of a new French effort for a cease-fire in Syria that would include a UN Security Council vote on Saturday. But it’s unclear what advantages his plan would have over the US-Russian led process that collapsed last month.

Kerry’s September 9 agreement with Russian Foreign Minister Sergey Lavrov would have created a new counterterrorism alliance in Syria, had fighting stopped for a week and aid deliveries been permitted to reach desperate civilians in rebel-held parts of Aleppo and other besieged areas. Neither condition was ever met.

The truce then shattered completely when Syria and Russia renewed their military offensive in Aleppo. Kerry ended bilateral discussions with Russia on the military partnership earlier this week.

Speaking in English, Ayrault called Syria a “human tragedy” that demands every effort to restart a peace negotiation.

Switching to French, he said Saturday would be a “moment of truth” at the Security Council. He said the question that will be posed to everyone, but particularly to Russia, is: “Do you, yes or no, want a cease-fire in Aleppo?”

Such a cease-fire would be “open to discussion,” but Ayrault said two demands were absolute. “The first one is the cease-fire and no fly zone over Aleppo,” he said. “And the second pillar is access for humanitarian aid. We’re not giving up.”

At the current rate of fighting, Ayrault lamented, “Aleppo will be totally destroyed by Christmas.”

Russia will almost surely veto the Security Council resolution.

The war has killed as many as a half-million people since 2011, contributed to Europe’s worst refugee crisis since World War II and allowed the Islamic State group to carve out territory for itself and emerge as a global terror threat.

Given the range of militant groups, extremists and outside powers now fighting in Syria, the original contest between Assad’s government and so-called “moderate” opposition forces has proven stubbornly difficult to quell.

Russia launched its air campaign in Syria a year ago, reversing the tide of war and helping Assad’s forces make significant territorial gains. Washington responded by engaging Moscow in a multinational process aimed at getting all of Syria’s fighting parties, except the Islamic State and al-Qaida, to buy into a cease-fire and eventual unity government.

The US also wanted Russia to join in the campaign against extremist groups like the Islamic State.

For that reason, Kerry and other US officials have tempered their criticism of Russia even as the death toll from its air campaign has risen.

Syrian human rights observers claim Moscow has killed as many as 9,400 people, crushing hospitals, schools and other civilian infrastructure in rebel-held areas along the way.

But by calling for the investigation, Kerry risks further shutting the door on diplomacy. Russia will likely be angered. And the Pentagon, which opposed plans for the proposed military partnership with Moscow, will likely find it even harder to contemplate cooperation with a government the US is publicly accusing of war crimes.

Russia, meanwhile, appears to be plowing ahead with its long-term strategy for Syria.

As Kerry and Ayrault spoke at the State Department, Russia’s lower house of parliament ratified a new treaty with Syria that would allow Russia’s military to remain indefinitely in the Arab country. The vote was unanimous.