While the United States continues to raise concerns about the Russian military buildup at an airfield south of Latakia, Mr. Kerry’s comments suggest the Obama administration is not confident it can persuade the Russians to halt the deployment — or impede it by persuading Syria’s neighbors to close their airspace to Russian military transport flights. The administration is focusing instead on reducing the risk of an inadvertent confrontation with the American-led coalition that is bombing the Islamic State in Syria.

The Tuesday phone conversation was third time this month that Mr. Kerry has spoken to Mr. Lavrov on Syria.

On Sept. 5, the United States asked a number of nations to close their airspace to Russian military transport flights.

But Iraq took no action in response to the American concerns. Russia has now deployed a small number of tanks, as well as artillery and armored personnel carriers at an airfield south of Lakatia. Moscow is also erecting housing that can accommodate 1,500 people. American officials are concerned that Russia will eventually base attack planes there.

Russia and the United States appear to remain far apart on what diplomatic action should be taken to stop the civil war in Syria. And Samantha Power, the United States ambassador to the United Nations, told reporters that they do not agree on the root cause for the rise of the Islamic State.