Two U.S. officials said Thursday that at least four cruise missiles fired at ISIS targets in Syria from a Russian warship in the Caspian Sea crashed in Iran.

The officials told CNN that some buildings have been damaged, and civilian causalities were reported in the crash.

The Russian Defense Ministry, however, refuted the claims, saying that all rockets fired from the ships found their targets. "In contrast to CNN, we do not talk with reference to anonymous sources. We show the launch of our rockets and the targets they struck," the ministry said in a statement, according to Reuters.

Russia claimed Wednesday that four warships of its Caspian Sea fleet had carried out 26 cruise missile strikes against 11 ISIS locations. The country's defense ministry also released a video of the cruise missile firings. See the video below:

"The fact that we launched precision weapons from the Caspian Sea to the distance of about 1,500 kilometers and hit all the designated targets shows good work by military industrial plants and good skills of personnel," Putin said in a televised meeting, according to the Associated Press.

North Atlantic Treaty Organization (NATO) Secretary General Jens Stoltenberg warned Thursday of a "troubling escalation" of Russian military activities in Syria. Stoltenberg, speaking at meeting of NATO defense ministers in Brussels, also slammed Russia for violating Turkey's airspace.

"We are in constant dialog and assessing the situation with Turkey, but the main thing is we have a duty to reinforce," he said, Bloomberg reported.

 "This will have consequences for Russia itself. I also expect that in coming days, the Russians will begin to suffer casualties in Syria," Defense Secretary Ashton Carter said during the NATO meeting, according to USA Today.