Russia has targeted Syrian rebel groups backed by the Central Intelligence Agency in a string of airstrikes running for days, leading the U.S. to conclude that it is an intentional effort by Moscow, American officials said.

The assessment, which is shared by commanders on the ground, has deepened U.S. anger at Moscow and sparked a debate within the administration over how the U.S. can come to the aid of its proxy forces without getting sucked deeper into a proxy war that President Barack Obama says he doesn’t want. The White House has so far been noncommittal about coming to the aid of CIA-backed rebels, wary of taking steps that could trigger a broader conflict…

“On day one, you can say it was a one-time mistake,” a senior U.S. official said of Russia’s strike on one of the allied rebel group’s headquarters. “But on day three and day four, there’s no question it’s intentional. They know what they’re hitting.”

U.S. officials say they now believe the Russians have been directly targeting CIA-backed rebel groups that pose the most direct threat to Mr. Assad since the campaign began on Wednesday, both to firm up regime positions and to send a message to Mr. Obama’s administration.