German Chancellor Angela Merkel says she is “horrified” by the impact that Russia’s relentless airstrikes on Aleppo, Syria’s largest city, are having on civilians.

And as Russia’s bombing campaign has killed hundreds and sent a fresh wave of tens of thousands of civilians north to the border with Turkey, Secretary of State John Kerry has exhorted Russia to heed a United Nations Security Council resolution from December, calling on combatants in Syria to spare civilian populations.

But that’s it.

The West’s inaction in the face of the recent Russian onslaught in Syria – which is in support of the army of Syrian President Bashar al-Assad – has several explanations, regional experts say. Those range from a desire to keep Moscow on board the sputtering Syria peace process to the emphasis by the United States and France, since the Paris and San Bernardino terrorist attacks, on the effort to degrade the so-called Islamic State.

But the key reason appears to be that no one in the West has the appetite to confront Russia as it pursues its interests in the Middle East.

“Russia has very clear intentions and is using military means to accomplish them,” says Heather Conley, director of the Europe Program at the Center for Strategic and International Studies (CSIS) in Washington. “At the same time our aims are not so clear, and we are using soft means to try to accomplish those unclear goals.”

The Obama administration has been caught off guard by the ferocity of Russia’s recent escalation in Syria, some say. But that surprise, they add, has only reinforced a determination not to end up in a conflict with Russia in a region that the US, under President Obama, is trying to play down.

“The administration does not like what the Russians are doing, but they’ve been set off balance by this recent escalation and they don’t seem to feel there is anything they can do about it,” says Andrew Tabler, a Syria specialist at the Washington Institute for Near East Policy.

Given Mr. Obama’s desire to stay out of Middle East crises as much as possible, he adds, “The US is not about to do anything that would involve going up against Russia and risk a confrontation in Syria.”

Russian President Vladimir Putin “has a plan” for rescuing Mr. Assad and reinvigorating Russia’s role in the Middle East, Mr. Tabler says, “and I don’t think they [the administration] care enough to do something about it.”

That “plan” appears to be on the verge of a major victory, with Russian-backed Syrian government forces – forces that were down on their heels just months ago – about to encircle Aleppo. That city once counted 2 million people and has been an opposition stronghold for much of Syria’s five-year civil war.

The US has no intention of going up against Russia militarily in Syria any more than it did over Ukraine, experts say, and so it is left to try to pressure Russia to curtail its indiscriminate bombing of civilian areas through diplomatic channels.

“The Russians are using a full array of military tools in Syria, as they have been in Ukraine, while the US and the Europeans, the West, are using the soft tools of humanitarian aid, some training [of rebels], and diplomatic initiatives,” Ms. Conley says. “We [the West] are hoping diplomacy will resolve this, but what we’re seeing is that the military tools are shaping the contours and the trajectory of both these conflicts.”

The US continues to insist that the Syria conflict will not be decided on the battlefield but will only be resolved through a political settlement encompassing all Syria’s political factions and religious and ethnic communities. That approach, at least officially backed by Russia, was at the heart of peace talks that got going briefly last week before being suspended indefinitely.

Meeting at the State Department Monday with Saudi Foreign Minister Adel al-Jubeir, Secretary Kerry said, “It’s our hope that because we [the US and Saudi Arabia] both believe in diplomacy that over the course of these next days some progress can be made with respect to Syria.”

The aim of that diplomatic effort, he added, will be “to move towards full humanitarian access and a full cease-fire” in Syria.

Another factor in the administration’s approach to the Syrian conflict, says Tabler of the Washington Institute, is the involvement of Iran. Following the deal with Iran last year on its nuclear program, the US is determined to be less confrontational with Iran, he says.

“The US is not entering into an alliance with Iran, as some in the region seem to fear, but it is giving [the Iranians] a free pass to do what they feel they need to do” in Syria, Tabler says. Iran has ground forces and advisers aiding government forces in the Aleppo battle, and Iran is seen as more intent on keeping Assad in power than is Russia, which above all wants to prevent a regime collapse.

The US inclination to avoid a confrontation with Russia over Syria may make sense to many Americans, Tabler says, but he notes that standing by while Russia pursues its goals could cause major problems for the US in the Middle East down the road.

“The Russians’ and the regime’s main trope has been that all the rebels are terrorists, and the Russians are on the path to achieving what they want, which is to make this a bipolar conflict between the regime on one side and extremists on the other,” he says. “But the impact of that [perspective] taking hold could be to force the legitimate opposition to rally behind ISIS and [other extremists] out of desperation.”

US partners in the region are increasingly questioning their ability to rely on a strong US presence, Tabler adds.

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Another danger that Conley of CSIS sees in Russia’s unchecked intervention in Syria is a further destabilizing of Europe by another unstoppable wave of refugees.

“This is not a primary focus of Russia,” she says, “but certainly [the Russians] would see a secondary benefit in the further fragmenting of Europe over the migration issue.”