The images released by Maxar Technologies, which has been tracking the buildup of Russian forces for weeks, could not be independently verified by Reuters.

The images also showed a new field hospital has been added to a military garrison in western Russia close to the border with Ukraine, Maxar said in a statement.

Russian President Vladimir Putin has ordered Russian troops into eastern Ukraine that he said were to keep the peace after Moscow recognised the separatist regions of Donetsk and Luhansk as independent.

US President Joe Biden responded on Tuesday by imposing sanctions, calling Moscow’s military moves “the beginning of a Russian invasion of Ukraine”.

Heavy equipment transporters, used for moving tanks, artillery and other heavy equipment, were seen near the Ukraine border in western Russia, as well as several new deployments of troops, according to Maxar.