WASHINGTON — Russian military officials have vociferously denied that their airstrikes have killed civilians in Syria, going so far as to say that eyewitness accounts that a major hospital was bombed last year in the brutal fight to retake Aleppo were mere fabrications.

But a new analysis that draws on satellite images, security camera videos, social media and even footage from the Kremlin-backed Russian television network has challenged Moscow’s claims that its airstrikes on behalf of the Syrian military were an exercise in prudent restraint.

The analysis shows that the hospital, contrary to claims by a Russian general, was bombed multiple times. It indicates that Russian aircraft used incendiary munitions and cluster bombs, despite the Kremlin’s denials, and concludes that Syrian forces used chlorine gas on a far greater scale than is commonly believed.

The analysis is presented in a report, “Breaking Aleppo,” which is to be made public on Monday by the Atlantic Council, a Washington-based policy research center. The report comes as President Trump has signaled an interest in forging better connections with President Vladimir V. Putin of Russia, which could include working more closely with the Russian military in Syria.