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 in a Wall Street Journal report.

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

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U.S. officials say they now believe the Russians have been directly targeting CIA-backed rebel groups that pose the most direct threat to Syrian leader Bashar al-Assad, partly to send a message to Mr. Obama’s administration, the Wall Street Journal claimed.

A spokesman for Russia’s Embassy in Washington contradicted these claims and was quoted in the article: “Foreign Minister Sergei Lavrov has made it clear on multiple occasions that the airstrikes are targeted at ISIL [Islamic State], Nusra and other terrorist groups.”

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U.S. officials say they believe the Syrian regime has been handing targeting information to Russia, the Wall Street Journal reported, adding that U.S. officials and rebel leaders said the White House has taken no tangible steps thus far to offer support.