The Russian Ministry of Defense said Friday that two ships from the country’s Black Sea Fleet, the Zelyony Dol and the Serpukhov, fired three missiles from positions off the coast of Syria in the eastern Mediterranean.

The Kalibr missiles are a new addition to Russia’s arsenal, similar to American Tomahawk cruise missiles. And like Tomahawks, they are capable of carrying nuclear warheads.

But taken in the context of the dozens of strikes that Russia carries out daily, the three missile attacks were hardly significant. The ministry said the missiles hit a garrison, a command center and a weapons depot belonging to the Levant Conquest Front, until recently called the Nusra Front and officially affiliated with Al Qaeda.

Far more important militarily is the decision to fly the long-range bombers from Iran rather than from Moscow as it had before; if it continues, this could result in a more devastating air war over a long period of time.

The United States, too, engaged in saber-rattling on Friday.

The Pentagon said it had scrambled aircraft over northeastern Syria in a warning to the government after Syrian warplanes hit areas controlled by Kurdish fighters that are working with the American military to fight the Islamic State. The government and the Kurdish-led forces have had only occasional skirmishes, maintaining a kind of de facto truce, and the government airstrikes came amid their most serious clashes yet.

Scrambling the jets was the most robust American response yet to Syrian government airstrikes, although Syrian and Russian attacks have repeatedly hit predominantly Arab rebel groups backed by the United States, as well as hospitals, schools and civilian areas. The American move prompted grumbling from opponents of Mr. Assad, who said that the United States appeared ready to offer stronger protection to its Kurdish-led allies than to other rebel groups or civilians.

Two SU-24 bombers struck Thursday near the city of Hasakah in north-central Syria, said Captain Davis, the Pentagon spokesman. No members of the American military were harmed in the strikes, he said.