MOSCOW — Ukrainian officials have been raising alarms about what they say is a huge buildup of Russian troops, tanks and artillery pieces along their border that could signal preparations for an invasion.

While the Russian military presence along the border is undisputed, some analysts have questioned its characterization as a buildup that might telegraph an escalation in the war in eastern Ukraine. Russia has quartered thousands of troops in the area for nearly five years. The United States and the North Atlantic Treaty Organization, while broadly voicing support for Ukraine, have not corroborated the claim of troops massing at the border.

The Ukrainians have pointed to commercially available satellite images showing rows of tanks and armored personnel carriers at two sites in southern Russia, and military transport planes parked at an air base in Crimea.

The Il-76 jets arrived at the same airfield, called Dzhankoi, where last month the Russian news media reported a new deployment of S-400 long-range antiaircraft missiles, among the most sophisticated weapons in Russia’s arsenal.