(Left to right): Russian Foreign Minister Sergei Lavrov, Russian President Vladimir Putin, and US Secretary of State John Kerry. REUTERS/Mikhail Klimentyev/RIA Novosti/Kremlin

On Wednesday, Russia began bombing Syrian rebels in a major escalation of the 54-month war that has the US searching for answers.

The bombing campaign, which apparently targeted rebels unaffiliated with ISIS, "completely bypasses every bit of legitimate discussion we've had with them so far," a defense official told Politico.

Russian President Vladimir Putin and US President Barack Obama had reportedly agreed about fighting ISIS and opening lines of communication between their militaries to prevent any accidental conflict.

But on Wednesday the Russians gave the US little notice before bombing rebel groups fighting the regime of Syrian President Bashar al-Assad, a close ally of Russia.

"This morning a Russian 3-star general walked across street to the US embassy in Baghdad and told them 'We bomb in 1 hour," the BBC's Paul Danahar tweeted. "'Stay out of our way.'"

Moscow even told Washington to avoid Syrian airspace, but US-led jets bombed ISIS positions near the northern city of Aleppo in the early afternoon and US State Department spokesman John Kirby said the anti-ISIS air campaign in Syria would continue.

'Capitalizing cleverly'

Moscow insists its warplanes are targeting ISIS — aka the Islamic State, ISIL, and Daesh — but US Defense Secretary Ash Carter told reporters that the airstrikes "were in areas where there probably were not ISIL forces."

The strikes apparently targeted the al-Qaida affiliate al-Nusra Front as well as US-backed rebels of the Free Syrian Army and Turkey-backed rebels of Ahrar ash-Sham.

"If true, [the bombing] suggests that Moscow is after much more than ISIL," Fred Hof, a former State Department policy planner on Syria in the Obama administration, told Business Insider by email. "Given the fact that the Nusra Front has managed to insinuate itself into much of rebel-held northern Syria, a Russian decision to go after this particular Al Qaeda affiliate would give it the ability to hit nearby non-Al Qaeda opponents of Bashar al-Assad."

Hof added that "it appears that Putin is capitalizing cleverly on the shortfalls of US Syria policy."

The Obama administration has been consistently reluctant to get involved in Syria, over the risk of being pulled into the brutal civil war. Assad is backed by Iran and Russia, which recently sent 2,000 troops and dozens of attack aircraft to Syria's western province of Latakia.

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'It's pretty remarkable'

Jeff White, a military expert and former officer with the Defense Intelligence Agency, told Business Insider that, unlike the US, Moscow is making bold moves to influence dynamics on the ground.

"The Russians don't care what we think. They've got a plan — they have an operation set in motion — and they're going to go ahead with it," White said in an interview. "They're challenging the US directly to respond, and they're exploiting the US weakness there. Russians are operating on their own timetable, with their own objectives, and they know what they want to achieve."

White added that Moscow is "betting that the US won't respond strongly. If the US begins to take a stronger stance on this, the Russians might adjust — but they just told us, 'We don't care what you're doing. We're going ahead.' It's pretty remarkable."

The options for the US are limited.

"As for what the US can do, it's late now, because we let them get away with all of this without any response at the outset, during the buildup. So now it's a matter of playing catch-up," White said. "We should say, you cannot fly in these areas, and demarcate them. Then we should say, 'If you do fly in those areas, we'll engage you.' We should also say that if you attack forces we support, we will protect those forces.

He added: "They would probably back down, but then again it all goes back to what kind of a risk-taker Putin is."

And Putin has already proven to be a risk taker.

"Putin sees opportunity and he takes it," Paul Stronski, a senior associate in Carnegie's Russia and Eurasia Program, said in an interview. "He is gambling on the idea that this war, and standing up to the West, will sell at home. But it's an extremely dangerous situation, and, so far, the Russian intervention in Syria hasn't proven nearly as popular as in Ukraine."

'New rules of the game'

Aaron Stein, a nonresident fellow at the Atlantic Council, told Business Insider that the airstrikes will likely "prolong the conflict, forcing the regional states to up their support for rebels."

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In essence, Russia's direct entrance into the war on Assad's side guarantees more chaos.

"All bets are off for any and all parties that had hoped for measures to restrain Assad's slaughter in Syria," Jonathan Schanzer, a Mideast expert at the Foundation for Defense of Democracies, told Voice of America.

"This includes the Turks, who had hoped for a safe zone. With Russian warplanes in the sky and other assets on the ground, Assad has insurance he has not had since the war broke out. Assad's adversaries will now have to wait for Vladimir Putin to spell out the new rules of the game," Schanzer added.

Boris Zilberman, a Middle East and Russia expert at the Foundation for Defense of Democracies, said by email that "Russian intervention in Syria has been and will continue to be about two things: Propping up their client — Bashar al-Assad and expanding their military presence in the Eastern Mediterranean and expanding Russian influence and power projection in the Middle East."

The head of the Western-backed Syrian opposition, Khaled Khoja, asserted that Wednesday's Russian air strikes in Syria killed 36 civilians.