BRUSSELS — Four cruise missiles in a barrage of 26 fired by Russia from warships in the Caspian Sea at targets in Syria crashed in a rural area of northern Iran, senior United States officials said on Thursday. Russian and Iranian officials dismissed the claim as nonsense.

It was unclear exactly where in Iran the missiles might have landed, or whether there had been any casualties or damage. The United States officials said the flight path of the Russian cruise missiles, called Kalibrs, would have taken them across northern sections of Iran and Iraq en route to Syria.

Of the initial 26-missile volley, the officials said, four went awry and hit northern Iran, according to technical sources of information like radar and satellite imagery.

The officials spoke on the condition of anonymity to discuss military intelligence.

News of the apparent crashes, which were first reported by CNN, came as Defense Secretary Ashton B. Carter sharply criticized what he called Russia’s “unprofessional” conduct in its incursion into Syria. Speaking at a NATO news conference in Brussels, Mr. Carter said that Moscow had fired the cruise missiles with no advance notice.