President Obama warned Friday that Russia's military engagement in Syria in support of strongman Bashar al-Assad is a "recipe for disaster," though Washington could still work with Moscow on reducing tensions.
Russian President Vladimir Putin "doesn't distinguish between ISIL and a moderate Sunni opposition that wants to see Mr Assad go," Obama told reporters, referring to the self-proclaimed Islamic State group.
"From their perspective, they're all terrorists. And that's a recipe for disaster."
Russia carried out a third day of air strikes in Syria, saying it targeted Islamic State jihadists, as Putin faced increased international criticism over his military campaign.
The West has raised concerns that Russian forces were also striking at rebel groups opposed to Assad, in a bid to bolster its ally.
Obama accused Moscow of "propping up a regime that is rejected by an overwhelming majority of the Syrian population."
He also said the United States would "continue to support" moderate rebels in Syria because they are groups that "can help pick up the pieces and stitch together a cohesive, coherent country" in the aftermath of Assad's rule.
Obama signaled he was willing to engage with Putin, particularly if Moscow "works instead to bring about a political settlement" instead of doubling down on its military support to Assad.
"I said to Mr Putin that I'd be prepared to work with him if he is willing to broker with his partners, Mr Assad and Iran, a political transition," Obama said.
"We can bring the rest of the world community to a brokered solution, but that a military solution alone -- an attempt by Russia and Iran to prop up Assad and try to pacify the population -- is just going to get them stuck in a quagmire."