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Barbarism. Mayhem. A New Hell. War Crimes.

The language of diplomacy has taken a turn over Russia's involvement in Syria, with the rhetoric crossing lines not seen since the Cold War.

A snap meeting of the United Nations Security Council on Sunday underscored the undeniable shift — one which has not gone over well at the Kremlin.

The U.S., U.K. and France — which called the meeting — walked out in protest when Syria’s representative took the podium, though not before firing parting shots.

We need to decide how to stop this. Now. #Syria's @UN ambassador is not interested in that decision. That's why I just walked out of #UNSC. — Matthew Rycroft (@MatthewRycroft1) September 25, 2016

Moscow has helped unleash “a new hell” on the city of Aleppo, Britain’s envoy told the council, saying “it is difficult to deny that Russia is partnering with the Syrian regime to carry out war crimes."

U.S. Ambassador Samantha Power said “what Russia is sponsoring and doing is not counter-terrorism, it’s barbarism.”

She added: "It is apocalyptic what is being done to eastern Aleppo. "This council can at the very least have the courage to say who is responsible for this. And, in a single voice, tell Russia to stop."

Russia hit back at the critique on Monday, with Kremlin spokesman Dmitry Peskov calling the tone “unacceptable.” Foreign Minister Sergey Lavrov dismissed the session as an attempt to distract from U.S. actions in Syria.

. @AmbassadorPower urged UNSC members to call out Russia pic.twitter.com/dmQPINFNxZ — Abigail Williams (@Abs_NBC) September 26, 2016

While the meeting itself ended with no actions agreed or undertaken — Russia does hold a permanent seat on the council — its significance and tone can’t be overlooked, according Europe analyst Alex Kokcharov.

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“This is much more than the usual diplomatic chitchat,” said Kokcharov, who works for IHS Country Risk. “This is significant — both the fact that the U.N. Security Council met on a weekend and also that they have used words such as war crimes.”

He said the language was “probably the strongest we’ve heard since the Cold War ended” in 1991 — and underscores just how much has changed since Moscow went into Syria. At the time, he explained, Russia’s goal was to rehabilitate its image on the international stage after its invasion of Crimea.

“Russia wanted to be taken seriously on any future discussions on Syria," Kokcharov said. "And therefore the fact that Russia is now playing its cards so much against what the U.S. and Europe want to see in Syria — it actually undermines these goals.”

Moscow has tried for months to position itself as negotiator, with Lavrov working closely with U.S. Secretary of State John Kerry.

But attempts to negotiate cease-fires have failed — and evidence mounted that Russia is not targeting ISIS as promised and instead focusing on wiping out opposition to Syrian President Bashar al-Assad.

Related: No Sign of Syria Cease-fire in War-Torn Aleppo

After the latest U.S.-Russia brokered cease-fire deal unraveled, the Syrian regime launched a fresh and brutal offensive on Aleppo.

That has prompted international outrage and also exposed the fragility of the Kerry-Lavrov relationship — evidenced by Kerry’s comments over the weekend saying that “patience with Russia's continued inability or unwillingness to adhere to its commitments is not unlimited."

“Russia needs to set an example, not a precedent — an unacceptable precedent, I might add, for the entire world,” the U.S. secretary of state told reporters.

But more airstrikes on Aleppo followed, pounding the rebel-held parts of the city in what activists have called the fiercest bombardment since the war began.

The ongoing carnage —replete with scenes of bloodied civilians in the streets, children being pulled from the rubble — prompted Western nations to call the U.N. Security Council meeting and ramp up the rhetoric.

And raising the prospect of war crimes at the U.N. — which are subject to international courts and also can be used to help justify sanctions — has significantly upped the ante.

Complete Coverage: Aleppo's Children

Kokcharov said he expects Western nations to call for more sanctions against Russia. Such measures helped deter further Russian involvement in Ukraine after Crimea and have hit Russia’s economy hard.

Taking another economic blow is probably the last thing Russia wants. So why then is Moscow placing itself at risk of the Western nations’ wrath? Because Putin is playing the long game, Kokcharov said.

“There is this expectation in the Kremlin that we just need to sit and wait it out,” he added.

“It” is a series of elections in key Western nations — the U.S., France and Germany, specifically — over the next 12 months. Putin, though, isn’t going anywhere anytime soon: his term isn’t due to end until 2018.

So while there might be calls for sanctions and concern about Syria, Russia is banking on the fact that domestic developments will make them less likely to push for them.

Western nations are concerned about Syria, Kokcharov said, but “they’re much more concerned about the electoral cycles in their own countries right now” so won’t be willing to undertake bold foreign policy moves.

And what does that mean for Russia?

“They have got into an expectation that in the longer run they can win by just waiting for change of leadership in key countries. Then they will be able to pressure the new leaders and new individuals who would be in power into accepting Russia’s rules of the game on Syria. Or on Ukraine. Or both.”